To "lock-down" my Ubuntu clients I use gconf. It's a set of scripts that tell the computer what access to give each person. You can either have this as a per computer bases or a per user basis, it has a frontend so you don't have to do it all by hand.
I use Linux as my main system at home and have done for 10 years, I also play alot of games....what ones are you talking about? I tend to use cedega/wine though....not native. Though the recent news is that Steam is releasing it engine for Linux so that their games will run natively. :
[Phoronix] It's Official: Valve Releasing Steam, Source Engine For Linux!