My guess would be the High Definition Audio Bus Driver, this is a microsoft driver and is different for SP1 & SP2 (the Realtek High Def audio driver sits on this bus).
Download the latest driver set from the realtek website and expand it out, you should have a MSHDQFE folder navigate to this then Win2K_XP\us , there will be 3x installer packages here that should look like this
kb888111w2ksp4 - This is for Windows 2000 SP4
kb888111wxpsp1 - This is for Windows XP SP1
kb888111wxpsp2 - This is for Windows XP SP2
to test the theory run the installer for the sp2 one and see if it cures your problem.
If all is well expand the contents of the update and browse to the commonfiles folder, here yu will find the driver files for the High Definition Audio Bus Driver SP2.
The other machines were not affected because they dont have HD Audio so they didnt have the BUS driver to be messed up.
Hope this helps, do let us know how you get on.