forgive me if i'm wrong, but it seems simple to me.
uninstall itunes 8.1, download and install itunes 8.0
to be safe, if you want to back up your songs you can find them in ~/Music/iTunes/iTunes Music, and just put itunes 8.1 on a jump drive and take it off your computer.
actually... now that i think about it a little more, just zip itunes 8.1 and download 8.0 and install. see if that works. if not you might move the zip file to a jump drive... if you have one.
wow i'm rambling... sorry it's late and i'm sick. hope that helps.