Depends on how many people play, and also how powerful your server is. You want tons of RAM and a fast CPU to act as a game server. You should be OK for 3-4 users with no issues as far as the connection goes. Maybe more, games don't use up that much bandwidth to play, most of the processing is in the local PC.
Ok thanks! My PC specs are as follows...
AMD Phenom II X4 955 3.2 GHZ (i can overclock to 3.9 GHZ)
4 GB DDR3 RAM (is this enough? i can upgrade to 8GB)
Radeon 4870 512MB
600W Power supply