Try moving the Microsoft User Data folder out of your Documents folder. If it runs fine after moving it, there was something in there that was confusing Office. If not, you can move it back, replacing the one that got created. The MUD folder contains your Entourage database, so if you use Entourage, you will need to move those databases back into the newly created MUD folder if that fixes the problem.
Another place for startup problems is in your Preferences folder ( in your user Library--to get there, hold down the option key and select Library from the Go menu in Finder). You could try moving anything with Microsoft in the name. Then see if it works. The preferences store all of the user settings in the programs. They will get recreated with all the default settings. If that doesn't fix the problem, I would seek help on the Microsoft web site.