a steam account doesnt give you the right to play any game under its flag
one cd key can only activate css for one steam account
the game itself should appear in ur game section once u have activated it , its often dark shaded if u havent install it
then u dont need the cd to install, u can simply download it through steam if u have the game activated in ur account
in ur situation , i think what u need is ur friend's steam account
Arh ok thks then...but when I tried to install it firstly I try putting in my own cd key and it says " You already have active subscriptions to the game(s) associated with this product code. You don need to re enter your product code, you simply need to log into this Steam account to access your games."...