I had this same problem awhile ago. The only way that I have figured out how to do this is:
Start>Accessories>System Tools>Backup
Back-up files and settings
Let me choose (choose files)
Make sure you don't click the button to "Allow only Admins and Owners access"
Backup, and then restore said files.
THIS TAKES FOREVER, BE PAITIENT.
The only time I did this was before SP1. I don't know if either of them changed it, but it worked for me. I'm not entirely sure its possible to DELETE the files that you are "backing up" once everything is completed. I compensated by just hiding them and choosing not to view hidden folders. A format would erase them though. Let me know if this works though.
Note: Also a good way to get into someone else's user files ; ) But I didn't tell ya....