I have a working faction system on my server.
Basically rhere are 2 factions, when a player joins they can choose one faction or get chosen automatically by a faction.
Each faction has their own main-world and freebuilding world.
Faction information is loaded from an .xml file at server startup.
I can give you the code but first check out my server, pm-ed you a link, if you like the system i can give it to you.
