yes if you have a legal copy from steam or from a shop you can i have purchased CS:S and Garrys mod together off steam so i can play Gmod.
Halo 2 source doesn't exist. It is also not offered on steam. Halo 2 will not work with garrysmod.
Omg .. Noob!
To manually place Counterstrike source files in GMod you will have to drag them either into the common folder or the folder with your name on it.
yes but dont use it because u get vac banned because im awesome
You put it in garrysmod\garrysmod\addons
3-5 hours
Go to windows explorer (go to my computer). Browse to where you installed steam. For example "C:\Program Files\Steam" and from there click on the folder called steamapps, then your username, then click on the garrysmod folder, and inside that click on another garrysmod folder, this is where the garrysmod files are. For example: C:\Program Files\Steam\steamapps\<username>\garrysmod\garrysmod
The latest one, Garry, the mod's creator keeps garrysmod updated. The current latest version in the Source SDK is 2009, though recently the "Source Engine MP option has become available" so use that if that is what the question is about.
I'm not sure which gamestartup file. But you can have background music when you start garrysmod, this file is gamestartup.mp3. The file can be placed here: <STEAM USERNAME>\garrysmod\garrysmod\sound\ui Hope this helps.
The best place to buy and play Counterstrike 1.6 or Source is through Valve's distribution application: http://store.steampowered.com/app/10/
on addons ( steam/steamapps/garrysmod/garrysmod/addons)
It should be able to play it perfectly.