No activity in the Macintosh world has ever inspired as much fear, loathing, and terror as contemplating the upgrade from Mac OS 9 to Mac OS X. People are worried they'll be forced to use the command-line (you won't) or that they must reformat and repartition their hard disks (it's not necessary). Others worry that they'll have to spend hundreds of dollars upgrading software (upgrades can be helpful, but aren't always essential) or that Mac OS X's well-publicized shortcomings will prove to be huge obstacles (only if you're entirely inflexible). Then there are the immovable obstacles - old hardware or mission-critical software or peripherals that aren't compatible with Mac OS X.
So the first step is to determine if you can upgrade to Mac OS X. If you lack a relatively recent PowerPC G3- or G4-based Mac, or you're reliant on software or hardware that simply won't work with Mac OS X, you can't upgrade. Similarly, if you don't have some spare time to install the new operating system and become comfortable with the new environment, you shouldn't upgrade - the task isn't hard, but if you don't spend the time up front to do it properly, you'll waste even more time later. No matter what, I strongly recommend that you not stress about the fact that you can't upgrade. Apple hasn't set the technical requirements of Mac OS X to annoy you personally, and the reasons why any given program or peripheral aren't compatible with Mac OS X are many and varied. In short, if you have a Macintosh setup that does what you need, be happy with that and don't worry about Mac OS X until it becomes unavoidable (as it will the next time you buy a Mac).
Set Expectations -- If you are ready to make the leap to Mac OS X, the most important thing you can do is to set your expectations appropriately. Apple's marketing materials would have you believe that Mac OS X will somehow change your life. It won't. It's a computer operating system with a graphical user environment - nothing more, nothing less.
For the vast majority of Macintosh users at this point in time, Mac OS X will not enable you to do anything you can't already do in Mac OS 9. Browsing the Web, reading your email, using a word processor or spreadsheet - the primary uses of computers are equally as possible in both operating systems. Until fairly recently, in fact, upgrading to Mac OS X meant losing capabilities for most Mac users. That's less true every week, luckily, and more important, we're seeing new software appear for Mac OS X that has no equivalent in Mac OS 9.
You will have to put some real time and effort into thinking about how you want Mac OS X to work, configuring it appropriately and installing the necessary utilities for interface extras without which you simply cannot use your Mac. Realistically, it took me roughly a day to do the basic installation of Mac OS X and parts of several more days before I'd done enough configuration that I could remain booted into it. Fortunately, it's easy to boot back into Mac OS 9 while you're finishing off Mac OS X's configuration, so you don't have to commit a huge amount of time all at once to the upgrade.
Another expectation you may need to adjust is the amount of control you'll have over the system and how much you'll know about it. Long-time Mac users have often built up idiosyncratic filing systems and ways of working that simply aren't going to mesh with Mac OS X's rigid directory structure and multi-user mindset. All I can say here is, get over it, or you'll just spend all your time being angry about a few nested folders - life's too short for that. Apple has been pushing us in this direction for a long time, first with the System Folder, then the special folders inside the System Folder, then the Applications and Documents folders, and so on. You may not like it, just as you may not like the way Mac OS X can make you feel like a visitor on your own Mac, but these are deep-seated design decisions stemming from Mac OS X's Unix underpinnings, and you'll simply have to accept at least some of them. Consider it a Zen thing.
It's also hard to accept that you're not going to understand what makes Mac OS X tick, particularly if you've built up a store of Macintosh knowledge across many years. My advice here is to think back to when you were first learning the Mac and remember how much fun that was (well, it was for me). I've quite enjoyed learning Mac OS X's quirks and developing new ways of working, and my years of experience have made the process a lot easier than it was way back when.
Survey Hardware -- Assuming that your Mac has sufficient CPU power to run Mac OS X, the next step is to evaluate your hardware setup to make sure your system will work with Mac OS X and, if necessary, determine what steps are necessary to make it work.
RAM is essential, and although it's not quite the steal it was recently, it's still sufficiently cheap that you should make sure you have lots. 128 MB may be the amount Apple recommends as a minimum for Mac OS X, but since memory is dealt with completely differently than in Mac OS 9, the more RAM you have, the better (up to about 512 MB for normal use). Check TidBITS sponsor dealram for recent pricing on RAM for your Mac.
As far as hard disk space goes, Mac OS X needs a bit more than a gigabyte for itself. Most Macs that can run it have hard disks of at least several gigabytes in size, but I'd say that if you don't have at least 2 GB free, you should either free up some space or consider upgrading to a new hard drive. That's what I did: I originally bought my Power Mac G4/450 with a 10 GB drive - the smallest available at the time - and when the time came to install Mac OS X, I replaced the almost-full 10 GB drive with a 60 GB Maxtor hard drive that cost about $125. (This isn't the place to talk about the specifics of that installation process; suffice to say that I found Accelerate Your Mac's information invaluable, if a bit rambling.)
Peripherals like printers, digital cameras, external floppy drives, SCSI cards, and tape drives are sticky wickets. Many perfectly functional but older peripherals are not compatible with Mac OS X, and may never be. I recommend determining what is and is not compatible with Mac OS X before upgrading - that information is usually available on the manufacturer's Web site or by calling tech support. If a device isn't compatible with Mac OS X, you have two choices. You can replace it with one that is, handing down or selling the incompatible device as appropriate. Or, if the replacement cost is prohibitive, or if there's simply no compatible replacement available, you can reboot back into Mac OS 9 when you need to use that device (assuming, of course, that it doesn't work in Mac OS X's Classic environment, which most won't). Obviously, rebooting in Mac OS 9 to use a peripheral isn't ideal, but knowing that it will be necessary is an important part of setting your expectations.
I recommend making a list of all your devices, and note which ones are compatible, which ones will require new drivers, and which will need replacing. For those that need new drivers, record the URL to the page where you can download those drivers.
Survey Software -- Once you've evaluated your hardware situation, it's time to do the same for your software. My experience is that most Mac users use more programs than they realize. Here's a trick that can help you determine which programs you really use in Mac OS 9. In the Apple Menu Options control panel, set the number of recent applications to track to 99 (the maximum), and then use your Mac normally for a week or two. When you think your usage has been representative, open the Recent Applications folder in the Apple Menu Items folder, view it by name, and copy the listing to a word processing document (select all the files, press Command-C, switch to the document, and press Command-V) where you can make notes.
First, delete from the list installers or other applications that you won't use again. Then, for the remaining applications, visit their Web sites and try to determine if you need an upgrade. If so, note in your list how much the upgrade costs, the URL to where you can get it, and if you'll be able to run the older version in Classic mode temporarily. For instance, I haven't gotten around to upgrading to the Mac OS X-compatible version of Timbuktu Pro, and for the few times I've needed to use it, it has worked acceptably in Classic.
As with your peripherals, if you have an application that you can't do without but which has no upgrade and isn't compatible with Classic, you have two options. Either reboot into Mac OS 9 when you need to use it, or find a replacement program. I won't pretend that these are good options - the main consolation I can offer is that most applications I've tried have worked fine in Classic. A few others, such as the heavily used QuarkXPress 4.1, are compatible with Classic but miserable to use. (When switching from another application to Quark, I recently discovered, you must refresh the screen with Command-Option-Period, something that's perhaps best done with a macro; also, if you're accustomed to switching tools using Command-Tab, you need to use Command-Control-Tab instead or try the Shift-F8 shortcut for switching between the two most commonly used tools.) I'm looking seriously at Adobe InDesign 2 for the next iteration of my iPhoto book.
Survey Interface Usage -- There's a class of software that has likely escaped your notice in the previous step - those invisible utilities that make life so much easier in a myriad different ways. Check your Control Panels and Extensions folders and add any utilities you rely on to your list of software, paying special attention to subtle bits like the Retrospect Client software, for which you'll need to upgrade Retrospect backup servers as well. And don't forget to note items that don't necessarily reside in your System Folder such as Palm synchronization conduits (located in the Conduits folder within the Palm Desktop application folder), which still don't exist under Mac OS X for many applications.
Also go back and read the articles I've written about the top Mac OS X utilities for ideas on how you can replace not just third party utilities, but also some of the aspects of Mac OS 9 you can't imagine living without. For instance, my father was flummoxed by Mac OS X's static Apple menu and the Dock; once we installed ASM and FruitMenu, his comfort level increased significantly.
Gather Software -- Once you've completed your lists of hardware, software, and interface modifications, I'd encourage you to go out and start downloading everything you can, purchasing programs like Microsoft Office X if necessary, and acquiring any necessary hardware. Obviously, there's no reason you must do this before installing Mac OS X, but doing it beforehand lets you do it at your leisure, rather than all in a rush after installing Mac OS X. Make sure to store all the things you're downloading together so you can get to them easily once the time comes to install. If you're not absolutely certain you will stay with Mac OS X after upgrading, feel free to put off purchasing upgrades to applications you can run in Classic or replacing peripherals that work fine in Mac OS 9.
If you have a slow modem connection to the Internet, not only will downloading these updates in advance remove stress after you installed Mac OS X, you can also get the various Mac OS X updates that you'll need, since otherwise you'll be stuck waiting for Software Update to download very large files as part of the installation process. Plus, should you ever need to reinstall, you won't have to download these installers again.
I'll cover more on that in the second part of this article, as we get into the nitty-gritty of preparing your hard disk, actually installing all this software, and taking your first steps in Mac OS X.