You're essentially configuring a computer as a kiosk. This is a problem I've dealt with more than a few times, and I've never been fully satisfied using mandatory user profiles and policies. It is a significant amount of work to lock the computer down to the point you need. I suggest that you use software specifically designed for kiosks. You can search Google for the keywords "Windows 2000" and "kiosk." -- here is a link to results from that search.
This was first published in July 2003