There are legitimate reasons - such as doing file maintenance and deleting folders that are no longer needed. These possibilities could be some of the $NThotfix$ folders, which reside in C:\WINDOWS or the Temp, Prefetch, etc.
Program Files has a folder in it called InstallShiled Installation Information which I like to keep clean as well
What?My two PC is XP Pro, both login as Administrator, all the drive can access except 'Program File' 'windows'. also all the drive which have this two directory is shared...