We did the same thing to our iMac and are stuck with the white screen. Did you find out if this is covered under AppleCare? We paid for the extended warranty and really don't know what to do if it's not covered. I'd like to hear the end of this story.
mate got his fixed under warrenty altho the people at the apple store where not 100% as it is beta software but they gave him the benifit of the doubt.
question did you install it with a manufacture version of XP ie. a version that has say Dell on it.... im pretty sure thats the problem as i tried it with a MESH disk i think and only one partition poped up with like 130 gig space or sommit luckily when i quit it worked lol.
make sure you use a proper XP SP2 disk or VISTA that isnt for a said computer brand....
oh and maybe dont tell apple you where installing bootcamp just say you restated your pc and the problem happened from there on in.