1) I like linux. Linux is free. Linux is so much more powerful than anything MS has, its like WOW.
Linux rules serverdom. PERIOD.
Linux has very poor game support.
2) Linux takes time to learn.
3) I'm still not sure what you are trying to do, in otherwords, what is a "game server"?
4) Senario A = one DHCP + internet connection sharing "server" = XP home. As many computers as you want can connect to the internet and play games. You can set up your own, "internal net" games, with as many players as the game will allow. For example, you can have 8 computers + the dhcp server, and ALL 8 can join a warcraft III game created by any ot ther other 8.
In this scenario, there is no real "game server" or game server software. You simply play the game, and any number of people can join. WarIII for example, only allows 8 people in one game. You could, however have an XP dhcp server, and have 16 people on your network, playing in 2 8 player games of wariii no problem.
5) Scenario BSome sort of "game server" where the game server runs some software. I am not familiar with this scenario. If the software really resides and runs on the server, and the game players need to run the software on the server, then I think you're hosed, as you can only have 5 folks run that software under XP. If, however, the server software simply sends stuff to the clients (position updates, etc.) and so the clients don't actually run the same sofware on the server, then you are OK.
My guess is quakecon runs linux or NT servers, probably multiple ones with some type of load balancing.
6) If this is the case, that the clients need to run the same software on the server, AND if there is a linux version of the server, THEN your best bet is linux.
7) I recomend you go to some gamers forum, and ask around there. It looks like not too many folks here at overclockers.com have set up a game server for more than 5 folks. There has to be a gamers forum where folks do this all the time.
Don't forget about us, if you do get an answer from a gamers forum, please keep us filled in.
My GUESS, is that xp will do what you want just fine.
Good luck