Counter strike MUltiplayer

[far]

Iv got this CS key from a friend which I can use to play counter strike online..The only problem is Im not sure which game to download..there are so many CS version out there...Can someone help me out with that?

thanx

[{I}{K}{E}]

you only need steam.

http://www.steampowered.com/index.php?area=getsteamnow