I think the consensus is, if you are going to dual boot, then XP on one, and Vista 64 on the other. I gave it a lot of thought and ended up going 64 Solo, and I've been very, very happy.
I do design work mostly, and neither Fireworks, Dreamweaver, or Photoshop have given me any problems. (Alright, Fireworks kills Aero, but its an old version of Fireworks, and who really cares?)