How did we get started talking about guild wars?
Cid: Guild Wars uses hybrid expansion packs. Basically, if you only buy the Prophecies campaign, then you can only play those missions. However, someone with Factions or Nightfalls can play with you in a Prophecies mission, no matter if it's a new exclusive character or not...as long as they have Prophecies as well.
I own all 3 anyways
But in general, I'm just thinking of using Xfire to organize multiplayer sessions, depending on which game everyone wants to play. If I decide to make the clan professional, then we'll worry about specific games