well let me put it this way. I once had Vista and it popped up with one of those "allow" screens....this was about the billionth time in around 2 months that it happened. i turned it off, slapped the Ubuntu install disk and completely formatted my computer and installed Linux.
In short, Vista is horrible, aggravating and the transparent title bars are really not worth hours of pain and agony clicking allow for every damn action you do. I dont know though, this could just be me and my short patience. But i personally would get XP as everything is compatable with it, there are no driver issues, its fast, reliable and also it does everything you want....well most of the things you want. XP has my vote.