1. Go to device manager and see if the USB Midi device has been recognised, and is showing to be working correctly. (If OK Go to 2)
2. Right click the desktop and choose personalise, select sounds followed by the playback tab and see if the Midi Interface is shown. (If it is not then it may not be compatible with Vista).
3. Setup a dual boot system to allow you to use both Vista and XP. (Alternatively ditch Vista and load XP)

Bill