Coooooool. I want to play!
If you really want to try it, get Half Life, it should be about 10 bucks, download the updates (free), install the Day of Defeat mod (free), get online and start.
For the money, you cant beat the action.
Get a headset with Mic so you can talk in-game and it is almost like being there.
Without the pesky mud and blood of real life of course.
Cheers,
knews hound