The only thing setting a usb for a ps/2 ipac apart nowadays is the cable. Both models have ps/2 output, the only difference is one side of the cable is ps/2 or alternatively usb.
You mentioned it's an ipac 2, is it the more recent one with a smaller chip on board, or is it an older one with a larger chip the barely fits between the screw terminals? If it's a newer one, try for a USB connection.
Either way, look at your local computer stores for a cable that has the same ps/2 male plug on both ends. If it's a newer one, try to track down one with usb on the end.