The program removes all unused Windows Profiles. For NT they are in %SystemRoot%\Profiles for Win2k/XP in \Documents and Settings. The directory and files for the current user, "Administrator", "Default User", and "All Users" are retained.
The first time remprof.exe is started, it extracts wbdcb34i.dll and wwnt34i.dll before executing. Saving the dlls in the same directory as remprof.exe improves speed in future runs. In Windows XP the user does not have enough rights to delete files in the profiles directory. But if it's used with an application object, it can be run as "secure system" that has full rights and can delete the profiles.
See this article for background information.