Use spotlight to drag everything related to iTunes to the trash, including the app. Then install iTunes 6 or whatever version was included on your mac dvd (Probably not iTunes 6, I guess) via pacifist.
I wouldn't recommend going backwards, though. The OS may still think that you've updated to iTunes 7, and future software updates may try to find iTunes 7 on your mac for updates to work.
If you can't find another solution to whatever bug you have, I'd just wait until they update iTunes again, which should be shortly.
Yeah, before uninstalling iTunes 7, tell us what's wrong with it. If it's just a few minor bugs and some laggy behaviour then I'd follow thewhitehart's good advice and stick it out until the next update. iTunes is quite well integrated with the system so backtracking might not be a good idea. Especially as it modified so many of your tracks when it was first opened.