and then get VAC banned, do you get banned from only that game or all your games? And does it run out or is it always permanent?
Your steamid is banned from *all* VAC secure servers running *any* source game. And they're permanent, only a handful have ever been revoked.
GMod dosn't run VAC in case your wondering VAC is like this All VAC bans a permanent, the only way to be unbanned is to make a new account and rebuy your games. VAC will only ban for known cheats, not things like materials or skins, only programs that alter game memory. If you are caught you will be banned for all games running that engine(If you cheat in Counter-Strike you can still play CS:S as CS runs the GoldSrc engine and CS:S runs the Source engine)
when Garry upgraded to EP2 engine he didn't like update his VAC to the new engine or something..so now it doesn't work or something like that. Basically you can cheat on gmod all you want and only admins will ban you since VAC isn't set up right. But since lua is easier to code in people make lua aimbots(ie Jetbot), and only uses real hacks for speed.