Software Installation Prevention

I have worked with this product in several libraries and schools. It works very well and has a host of configurable options. It is called FoolProof Security.

Regards
Martin
http://www.smartstuff.com/fps/fpsinfo.html

I use a product called GoBack (www.goback.com) on my general public machines. They have free 30 days trial versions. It doesn't prevent users from adding software. What it does do is make periodic snap shots of the workstation. Then depending on howyou configure it, it can always 'go back' to a specific time period, removing all changes and restoring the workstation back to the original condition (even if someone deletes their windows directory, woo hoo).
You can even set it up so that it will revert on a scheduled time (say at 6 am before everyone gets in) or whenever the machine reboots.
Of course this may not be a viable option if important files are kept on the workstation, and not file servers.
Hope that helps, good luck.