You know let me breathe some new life into this discussion.
I've got the MBP w/ an 80gb hdd. I can only spare 10gbs for xp and im out of space at that. I've got an external 2.5 drive that I'd LOVE to use as an xp drive.
I think what the OP was eluding to when he asked for more comments was that the Mac community is infamous for wanting to do something and pulling together and getting a solution out to the masses. Telling him that "its a definative answer" and trying to close it is ... I don't know.. rude I guess, especially when there are other people in the same thread saying otherwise. I'm sorry if this forum doesn't have the answer, but that doesnt mean that others don't.
As for my own research, AH, I'd say yes... its possible, but you'll have to work at it. Read the links above and see what happens. I would assume that yes, eventually Apple will see thelight and give users the option to boot from an external drive. Apple has been famous for that ability for years with the powerbooks and such. Just remember that Google is your friend. Don't let people tell you something isn't possible.
Look at the MBP's and the heat issue. People here have been saying since their intro that there was no solution, but I found one on another forum and postedit here!
Good luck,
J