Not very useful answers. Usually the point is to find the problem, not trying all kinds of random things until something happens..
Do you have this installed:
http://support.microsoft.com/kb/895980 This is practically guaranteed to be a problem with XP and many dual/quad AMD CPUs.
Enable on screen leds (misc panel).
Check CPU% snd SND% leds. Does CPU% stay constantly over 100% and how much or does it jump around?
Disable sound: does it still do the same?
Also 2.4.0 has slowdown problem if software filters are enabled.