Office 2004 includes an auto update mechanism, so you should be alerted of the update in the next couple of days. You can also force it to check for updates from the help menu of any of the Office applications.
Office 2004 is the first Microsoft Macintosh product to include a version of the Watson technology that sends crash reports back to Microsoft. This is an awesome technology that lets us learn about crashes that we never saw in our test environments. We also good statistics on how many people are hitting which bugs and lets us focus our energy on fixing the right bugs.
If you were running into any stability problems with Office 2004, there's a good chance you'll see them fixed in this update.