Do you want to downgrade from iTunes 8 to 7??
I gave you a link with info about downgrading, check post #2. That link has info about downgrading from iTunes 7 to iTunes 6...see whether the same things work when downgrading from 8 to 7.
Do you have an old installer saved? If not, you'll find links to download older versions of iTunes here:
Old Version of iTunes Download Thread merged with your original thread to avoid confusion.