Locking down the Registry…

I would like to accomplish two things. First, I want to prevent users from installing/uninstalling software. The second then that I would like to do is prevent the users from making changes to the registry. Here is the tough part. We are runningQuark 4.1. If we take the users out of the ?Power Users? group, then Quark will not run. Is there any thing that I can do? Is there any software, shareware, or freeware that any one can recommend? Thank you.