Same issue here - jumpy mouse and scratchy music when copying large files. I have an MSI nforce4 board but i'm running Leopard from an IDE harddisk.

I customized my install iPC 10.5.6 with the following things:

9.5 Voodoo Kernel
Legacy Time Machine
NVDarwin
Apple NForce
ACPI Fix
Firewire Mount Fix
IOUSB
SATA Drive Fix
Dual boot sync
IOPCIFamily
IOPCMCIA
Seatbelt
Shutdown Fix
UUID Fix
Apple SMBIOSEFI


Any hints for that problem? It's really annoying!

Thanks in advance
..