If you've run the installer, you must have SP2 installed, I would think. One last thing you might try is to also drag the rest of the files in the Preferences > Microsoft > Office 2008 folder to the desktop and try again.
You could also download Onyx (make sure you get the version for Mountain Lion). It's free and makes it easy to delete system caches and search for corrupt Preference files.
If none of these work, then yes I'd take it to the Genius Bar. They may balk at helping you if they think it's an Office problem. I'd recommend framing it as a User account issue. Tell them it works in a new user, and can they help you clean up your exisiting user so it will work there, too?
In any case, don't put those files from the desktop back. Just drag them to the Trash. Good luck. Keep us posted in this thread.