I would use a good live-cd that has gnome or kde. Make sure it has updated software and stuff. The best part is that if you want to put on a new version, just burn a couple more cd's. If a user screws up the system, reboot. Make sure that the bios is set password protected and only boot from cd. I would also have the tower hidden so they cant steal the tower and you might want to have a external reset button on the desk.
Good luck.
Good luck.