i could be wrong here (that's the usual caveat), but my understanding is that itunes doesnt use registry locations for your media files.
rather, it uses the itunes folders in your user profile (my music\itunes, app data\apple\etc etc) where it maintains in xml format, your target media file locations.
so if you delete / rename said folders, you should have a clean itunes install again... just saying, before you go about tearing up the reg
EDIT: some paths to get you started:
\My Music\iTunes
and within AppData (I think it's Roaming), Apple Computer\iTunes