MP3s skipping

Some of you may remember my ACPI thread - well, here is an update after I reformatted the computer:

Ok, here is the basic situation...

All of my music (mp3, games, streams, etc) stutters during playback. I don't know why or when this started occurring.

This is my system:

Windows XP Home
P4 3.0gHz
2GB RAM
10k RPM hard drive
Sound Blaster 5.1 PCI sound card, bottom-most slot
Latest drivers for all devices
4GB page file, only 277MB used
2-4% CPU usage at any given time
Sound card on IRQ 18 with SATA hard drive controller

This is what I have done to try to combat the problem:

1) Defrag
2) Download the newest drivers for everything
3) Try different program (WMP, RealPlayer, iTunes, etc)
4) Move the file to different hard drive
5) Scan for spyware using Hijackthis, Ad Aware, Spy Sweeper, and MS Defender
6) Move the PCI card to a different slot (won't work because of ACPI)

UPDATE!!!!

7) I did a complete re-format and re-installed Windows. It seemed to work and then eventually started skipping again. I think there might be an update or something...or maybe I just didn't hear the skipping when I completed the reformat.

What the heck can I do????