Any Source Game
Preferably CS:S as most gmod users have this
If you can atleast Run Half Life 2 you can run it.
No, you do not need to be on the game you bought with Gmod to play it although you do need to have the game installed to run gmod and i also recommend having the game Half-Life 2 installed to get most of the textures and weapons and npcs and props that go along with it.
Worst? Commodore 64.
Yes
no. gmod is only for the pc.
No. Gmod is only for PC
You need to download Gmod 9.0.4c when you start there will be 3 choose unmark the Gmod 9.0.4b and your set to go and play gmod 9 online.
Yes. I have Windows 7 and I play GMod all the time.
No, the Air can not run GMod because it doesn't have a level 9 graphics card.
Gmod 10 is a pay game. It can be purchased from the Steam store at http://store.steampowered.com It costs $10
you click the shortcut icon er the gmod .exe/file!
NO