i was told, over at another site (not in very specific detail, mind), that despite the fact that theres no kmixer in Vista, it would still resample, for the worse.
However, im just throwing this out there. i personally have no idea about this and, as i say, the person who told me wasnt very specific, they just said they think it happens.
if it doesnt, however, this would presumably mean, as has been said, that theres no difference between a suitably specced pc and a mac, wouldnt it.