If you have Counter Strike...then don't get Condition Zero. It is the purchased version 1.6, which you can download from the net for your 1.5 version.
Farcry is gaining popularity.
But the best bet for the buck, plus it is a great game is BF1942. BF1942 -Vietnam is the lastest version. I have the original BF1942 plus the Road to Rome expanision and love it. A lot of players still play this game.
Chronicle of Riddick...is not out for the PC...I think it is only the PS2 at this time.
And Joint Operations is getting outstanding reviews. I am playing the demo version now, and it is not your everyday first play game. There are so many controls it will blow your mind. However, this game is VERY demanding on your hardware so you better have a great computer.
Of those three choices I'd go for Far Cry, it really is a beautiful game.Not a bad storyline either.Today I'm getting 3 extra IP adresses and 1 new connection for my custom rig(finally).So I'll let you know how the multi-player is.....