removing NTUSER.dat

Hello everyone.

I know this is an old problem that's been asked a million times. But the solutions given a million times don't seem to work for me, so here I am asking it anyways.

On several computers at work, there are a lot of old, unneeded users. Previous volunteers/employees and such. Some are local accounts, some are roaming accounts from the old domain we're replacing.

I know that a good way to delete users is through My Computer> Advanced > User accounts. There it lists all the users in the system and their profile, with a big shiny delete button. Seems simple enough.

However, a lot of them are marked as "account unknown" rather than an actual username. The delete button for these is greyed out. After deleting all those I could, I go to C://documents and settings to see what's left/ Sure enough there are plenty of folders for old users.

I want them gone, but of course windows isn't having that. "Cannot delete NTUSER.dat. Another person or program is using it. Please close any applications that may be using it and try again."

Off to google I went for the answer. And the answer that comes back, repeatedly, is to take ownership of the file as local administrator, then delete it. I have of course tried this, and it does nothing. Noooothing!

The other prominent solution I could find was to install the Microsoft User Profile Hive Cleanup service, which I did weeks ago for other reasons relating to domain logons. It's not helping.

What I want to do is pretty simple. I want those users cleanly gone, in a way that doesn't require reinstalling the OS. We want nothing left except the built in accounts (Administrator, guest, "all users", anything else that would be bad to delete.)

I could probably boot with an ubuntu CD and just wipe non-system stuff from the documents and settings directory, but I'm guessing that would still leave the users' registry entries behind populating the list and may break something, so I'm asking for advice before doing that.

What should I do ?