Red Hat / Fedora :: How To Lock Down User Desktop

I work for a local community college, and we currently have web kiosks set up around the college. They have fairly old hardware and are currently running windows XP. However, with all the group policies and scripts required to lock them down, it can take 10+ minutes for the students to log in(we want authentication for someone to be able to use them).

Now, I have managed to get a few test computers to run fedora with openLDAP authentication and LTSP giving them a desktop with firefox. Now, the problem is that we don't want the user to be able to do anything but run firefox and, on some of them, print. I have been using gnome, gconf, and sabayon(not the distribution, the user profile tool) to attempt to lock down the desktop. However, anyone can just right click the gnome menu and add back in everything i disabled. While they wouldn't be able to do much harm, the point is that if they want to do work, we want them to go to our computer labs, instead of the kiosks. The kiosks are just for looking things up or getting on their e-mail.