In the device manager, can you select update driver (or rollback) and get it to search on the Windows Install disk?
Alternatively, you could use the Device Manager to 'Uninstall' your USB ports, and then allow Windows XP to locate them (as if you had plugged in a new PCI Card) and automatically load the drivers. The USB ports don't work anyway, so it might be worth a try...
Third alternative is to log onto the net and see if you can locate the drivers for your particular MoBo - they will also include the USB drivers. Reloading the MoBo INF files may also fix the problem.
Hopefully I've actually given you some ideas!!!