No because Garrynewman has not made l4d contact for gmod but if you type gmod in google you will find Garry's mod.org and click then type l4d and it shows l4d stuff
I deleted some last time, but I can't Rember what key I used...
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.
piggymoo.com has all of stargate, but I'm not sure what gmod is.
gmod 9, yes gmod 10-no
Download the playermodel addon from the workshop
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.
I would recommend garrysmod.org
download them on garrysmod.org, or port them mingebag
download them from garrysmod.org
go to steam.com here are some links related to Gmod to help you: Steam: http://store.steampowered.com/ Download stuff to Gmod here: http://www.garrysmod.org/downloads/ About Gmod: http://www.garrysmod.com/about/ Gmod fourums: http://www.facepunchstudios.com/
go to garrysmod.org (Not all of the girl stuff)