Need Help with online gaming!

i was trying to play some online games last night with some friends and it wouldn't work. i wanted to know if anyone knew how i can do it if its possible. I have a cable connection on a win2000 machine 2 network cards in that machine, 1 for the cable modem and the other pluging into a switch.the other 2 computers are hooked up to the switch. the internet is working on all 3 machines i was just wondering why i can't play online games with all 3 at the same time when they can do everything else online at the same time.