No, L4D2 was it's own game. It was just made by Valve on the Source engine.
Steam is the company that has created Counter strike, half life left 4 dead and many other great games like garrys mod ect.
No, Garry's mod only runs through steam and at the current time only supports: Half-Life: Source Half-Life 2 & Episodes 1 & 2. Half-Life 2: Deathmatch & Lost Coast. Day of Defeat: Source. Counter-Strike: Source. Team Fortress 2. Left 4 Dead. Portal.
Only for the half life 2 version of garry's mod.
probably Garry's mod
There are a few sites, check out the Left 4 Dead forums online.
Nope the game developped by steam there for its like CSS Half Life Left For dead ect it belongs to steam you will have to get it from store or download through steam if not it will be illigal and we cant help you with that here.
you can't without a mod
half life 2counter strike sourceleft 4 deadleft 4 dead 2garrys mod
Yes
yes
Yes you do. Counterstrike: Condition Zero, however, is not a mod of Half Life, and therefore, does not need Half Life to acquire.
there isn't its a mod in half life