You are talking about on a cab right?
Xp 64 all the way. Win 7 takes up too much resources and it has issues with unsigned drivers and all manner of minor annoyances. Win 7 is a better OS all the way around, but when you are building a cab you don't need any of it's improved features.
Also for the record, win 7 64 bit is the superior version, the 32 bit version is identical to the 64 bit only.... wait for it.... more bits!
