Condition Zero is single player. Or you can make your own game with bots. As far as torrenting goes, Steam will catch you right away if you play online.
Yes, apparently you knew what I meant, since you corrected me.
I don't usually pay for offline games, but go ahead and try to play CS:S on good servers without Valve disconnecting you for not having a "valid Steam logon."
Why would i want to play CS:S? That sucks compared to BF2142 wich i think is one of the finest online games ever created. Graphics could be better though.