I don't know if this effects all people with creative sound cards but if when you play mp3s they suddenly slow down for no reason this is what to do:

(win xp)
open control panel
open system
click the hardware tab
click on device manager
open sound,video and game controlers
doubble click audio codecs
click the properties tab
find ctmp3.acm and doubble click it
select do not use this codec

that should fix your problem

I posted this here because i took me ages to find this out and hopefuly it will solve someones problems. 8)