I found an helpful tool to reduce unused user profiles on network PCs. Typical example are shared computers used by different people in the same office.
The User Profile Deletion Utility (Delprof.exe) by Microsoft is a command-line utility designed to free up disk space in computers running Windows 2000, Windows XP, and Windows Server 2003.
delprof [/q] [/i] [/p] [/c:\\computername] [/d:days] [/?]
/q runs DelProf in quiet mode, with no confirmation for each profile to be deleted.
/i indicates that DelProf should ignore errors and continue deleting.
/p prompts for confirmation before deleting each profile.
/c:\\<computername> specifies a remote computer name on which to run DelProf.
/d:<days> specifies the number of days of inactivity (days is an integer).
Profiles with longer inactivity will be deleted.
/? displays command-line syntax