Hi!
I'm pleased I found someone with my identical problem (mouse and sound stutter during hard drive access) - just wish someone had the solution.
I have:
Dell Dimension 8250 - P4, I850 chipset
WinXP Pro
Soundblaster Live
ATI All-In-Wonder
Promise card from Western Digital w/ 2nd hard drive attached
I believe it is small writes to the 2nd hard drive that are to blame. Reads from the drive do not stutter the system and Explorer writes of large files don't seem too bad either). I suspect the card's driver/BIOS but Western Digital doesn't have a newer versions of these - Promise however, does but they warn folks not to try to use theirs unless you bought a Promise card outright (i.e. Western Digital users are out in the cold). I'm about ready to try it anyway, but I'd have to backup a ton of stuff to do it, so I'm a bit wary. Would you like to be the guinea pig?