Back door key strokes

I have set a mandatory profile and group policy for students at my school where they have no menu access to windows explorer and no icons on the desktop. They can only open applications in their edited start menu.I thought this would stop them having access to the local drive through explorer. However, some have found back door key combinations that let them bring up explorer and in some cases double cliccking on the start menu will do the same. Is there some source that lists all the back doorkey strokes in win2000 or a way to stop this happening?