So, Excel and PowerPoint v.X are crashing on me at launch. Word and Entourage aren't. This hint unfortunately didn't help the situation. So, after some searching on Google Groups, I saw a post about QuickTime extensions causing Office apps to crash, and they also mentioned the Toast VideoCD extension. I removed that one, but it didn't fix my problem.
It turns out it was the DivX 5.0.6 beta plugin that caused all the problems. Upgrade to 5.0.7 and you'll be set.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031008195506212