Microsoft released updates to both 2004 and 2008 versions of its flagship Microsoft Office for Mac, citing stability and performance improvements in both cases, as well as fixes for vulnerabilities in the applications. The updates are available immediately at the as well as via the Microsoft AutoUpdate utility (remember that each version of Office has its own version of Microsoft AutoUpdate).
Microsoft's release notes say the improves stability when opening Word documents that contain a numbered list and updates the Japanese postal code dictionary, in addition to fixing vulnerabilities that an attacker could use to overwrite the contents of your computer's memory with malicious code. The  fixes the same vulnerabilities, fixes an AppleScript issue that prevents running a script from the Script menu without restarting the Office application, speeds up opening the Word application for users with lots of fonts, improves the display of text in Word tables, fixes an issue opening Excel documents when some sheet names include invalid characters, improves number formatting in Excel for some international languages, fixes duplication of events between Entourage and iCal when syncing, and includes several other small changes.
The Microsoft Office 2004 for Mac 11.5.1 Update is a 15 MB download, and the Microsoft Office 2008 for Mac 12.1.2 Update is a 160 MB download. Because both updates repair significant vulnerabilities in Microsoft Office that could leave your computer open to attack, we recommend updating your copy of Microsoft Office immediately.
On the same day, Microsoft told us about a special promotion offering (the discount depends on the selected edition) when purchased along with a Mac from participating resellers through 08-Sep-08. The press release implies the discount is available to students and educators, but a visit to the  linked from the Microsoft page suggests no such restrictions on eligibility.