Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I don't know if this is the most efficient way, but the way I had to do it when changing my product key (I thought I would just use my roommate's product key... but alas, it didn't work) was uninstalling Office 2008, deleting everything in ~/Library/Preferences/Microsoft, and then reinstalling Office 2008.
 
I don't know if this is the most efficient way, but the way I had to do it when changing my product key (I thought I would just use my roommate's product key... but alas, it didn't work) was uninstalling Office 2008, deleting everything in ~/Library/Preferences/Microsoft, and then reinstalling Office 2008.

Thanks a Lot
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.