Re-reading you question it looks as if you know most of this (sorry, not trying to teach a granny to suck eggs!)...
Basically, there must be a way to change where ITunes looks for the database file... try searching the registry for the full path name ie. "C:\Documents and Settings\<USERNAMEHERE>\My Documents\My Music\iTunes\iTunes Music Library.xml"
Alternatively, to answer the original question, please refer to the following microsoft article:
http://support.microsoft.com/kb/884739