Check out deep freeze from faronics corporation. It allows you to let users
have administrator rights and do anything they want to the drive (including
deleting the registry, deleting critical windows files). All you have to do
is reboot the system and it will return back to the "frozen" state (the place
that you last froze the machine). But with a simple keystroke and password
you can "thaw" the machine and make necessary system changes (updating
antivirus, windows updates, etc.) We have the enterprise edition where I
work that allows systems to be "thawed" and "frozen" remotely by a server
console. It's awesome software. We live by it on all of our student use
computers.
