i've heard, but don't have any real info or links right now, that win xp does sounds kinda odd depending on your speakers/headphones. I think there is an option in there somewhere about digital speakers (as opposed to analog?) that you have to check off or they won't work.
Like i said, i don't know for sure where i heard this (i think it was The Screen Savers), but it was about laptops that wouldn't play sound b/c they had digital speakers but weren't checked off to play it.
Maybe i just had a weird computer dream and i'm pulling it straight out of my ass, but if it helps could you please confirm this?