First of all if you go XP then absolutely do not go 64 bit edition.
I would also shy away from 64 bit for now just for the simple fact that software support is horrid still. Its going to take a while at the current rate for that to change too.
As for Vista or XP this seems to be preference driven but I hear far more fuss from Vista users than XP users. I'm sure in part due to XP being more well known, but what does that matter when you are trying to do a project and it needs to be done NOW!
So ya I would go with XP, but I am sure others would say Vista.








