According to GamesIndustry.biz, Guild Wars: Factions will be “playable as a standalone game, but gamers who also own the original Guild Wars will be able to explore both game worlds and also get access to new items in the first game.”
GameSpy’s interview with Jeff Strain, Founder and President of ArenaNet. There are screenshots of the Ritualist and the Assassin as well.
In-game chat with Gaile Gray, Community Relations Manager at ArenaNet.
Thanks, Clamatius for those last two links!