Windows XP was released in 2001. Did you forget? My "old ***" sound card is has at least 3 years on top of the OS.
AHH! I never even accounted for codecs. Updates to XMMS keep the LAME and Vorbis library up to date, while Winamp 2.95 still uses the codecs it came with. I feel totally stupid for not realizing that. I guess then I should update my codecs in Windows.
XMMS on Fedora sounds really good too.