What I'm taking about is more or less games that take control of the entire screen not apps that enlarge to cover the entire screen (get it?)

As for useing a differnt VNC program I use RealVNC. Unlike desktop sharing it never times out and you can set passwords.

Only problem is you can't share display :0 (the one that basic users use)

However you can do cross system controls (windows to linux, linux to windows, etc) which I don't think you can do with Desktop sharing. ANd yes, you could take control of a student PC without there permission.

But I think that RealVNC's beta version is useing a hack to let it display :0

As long as on the topic what is the 0 and the .0 in :0.0 IN detail please