You need to affect the way it's assigned and being read. He may also need to get upgraded drivers for his GPS or serial-GSA converter so that the device is read not as a mouse or other pointing device.

I think starting with figuring out if you can manually adjust the Com port or IRQ -- or if the simple fix of deleting the item as a pointing device will work would be my approach to the problem.

Obviously, Dan y's and Andy's process may produce an acceptable result. In any event, I'd have the Device Manager up when I plugged in the GPS/USB device and see what's happening.