dont think it will be xp pro its self and i dont think xp home will make any difference, a clean install will wipe EVERYTHING on your hard drive and re-install windows, if that didnt sort it, then a new HD wont do any better.... have you always had this problem?
did it occur only when you updated to directX 9?

see if you can find this file: C:\WINDOWS\SYSTEM32\drivers\GM.DLS
if its not, try searching your computer for it...

click start> run and type in 'dxdiag' without the quotes and press enter
go to the music tab and see what it says next to 'General MIDI DLS Collection'

hope this helps,
mike