I'm a long time lurker on the mac rumors forums. I'm the leader of a clan that plays Halo and other games. We have a dedicated server for halo hosted through nuclearfallout (as well as UT2004 and CS: S). Feel free to play on our Halo server anytime you want as we rarely play Halo anymore so it's empty most of the time (it's up 24/7). It's a 16 player public dedicated server, hosted in San Jose, Ca, and has a fairly large map cycle rotation -- several maps of team based slayer and CTF, and a couple of king of the hill and race.
The server is named IDIC and has a direct IP of idic.nuclearfallout.net . I can change the map cycle and the gametypes if you wish (i.e. currently there are no tanks or shees on any of the maps in the cycle).
- (IDIC)Spock
www.idic-clan.com