Avoid Current Firmware Updates -- Apple's just-released firmware updates (4.1.7 and 4.1.8) for recent iMacs, plus the iBook, G4 Cube, Power Mac G4, and PowerBooks with FireWire ports have caused much gnashing of teeth. The firmware updates, which were released both on the Internet and on the Mac OS 9.1 CD-ROMs that come with Mac OS X, claim to make improvements to FireWire target disk mode, network booting, gigabit Ethernet networking, and overall stability. They also enable password protection of Open Firmware booting to increase the security of Mac OS X (which can protect its files via user privileges, but can't do so when booted from Mac OS 9). The significant problem with these firmware updates is that something in them can prevent the Mac from recognizing some RAM modules from third party vendors. Apple has yet to make an official statement about the situation. Our advice: don't install these firmware updates until there's word from Apple. [ACE]
Extract Directly from Time Machine
Normally you use Time Machine to restore lost data in a file like this: within the Time Machine interface, you go back to the time the file was not yet messed up, and you restore it to replace the file you have now.
You can also elect to keep both, but the restored file takes the name and place of the current one. So, if you have made changes since the backup took place that you would like to keep, they are lost, or you have to mess around a bit to merge changes, rename files, and trash the unwanted one.
As an alternative, you can browse the Time Machine backup volume directly in the Finder like any normal disk, navigate through the chronological backup hierarchy, and find the file which contains the lost content.
Once you've found it, you can open it and the current version of the file side-by-side, and copy information from Time Machine's version of the file into the current one, without losing any content you put in it since the backup was made.