Microsoft has available the Shared Computer Toolkit for Windows XP. Mostly designed to protect computers that are used by the public, it provides a higher level of security, such as restricting some users further from fiddling with system settings.
I wonder if it gets around some of the issues of most users not running as Administrator. I still haven’t found a satisfactory way of running MS Train Simulator except as Admin.
It also has something called Windows Disk Protection, which means any changes to the disk are lost on the next reboot. Could be handy. Of course, a less-than-scrupulous person might use it for wiping out expiring Shareware needed only sporadically. But a more legitimate use would be for trying beta software, to ensure your machine was in a pristine state afterwards.