Some friends of mine are putting together a massive lan party (50-100 people). They've rented out a entire room, and have assured me the party will be mac friendly. You can see their page at:
http://shorelinelanparties.tripod.com/
Please don't direct questions to me. I'm not organizing the party. The network is 10/100 with T1 internet access. Its in Shoreline, Washington, just 20 minutes from downtown Seattle. On the mac side there will most likely be AoE2, RTCW Test 2 (or final if its out), Starcraft, and of course Quake 3. Be sure to read the rules on the page. I'll be there if you're wondering (I know, I know, you can calm down now... no need to get excited).
Admins: Didn't know where to put this sort of thing, so move it if you wish.