The production of the MIDI interface "USB-2-MIDI" has been discontinued in the year 2000 and drivers for current Windows XP/Vista and Mac OS X systems are not available from Steinberg Media Technologies. Since the device is identical in construction with the M-Audio MIDI interface "MIDISport 2x2", drivers for that interface can be used with the "USB-2-MIDI" as well.
On the M-Audio website you can find compatible downloads for the following operating systems:
Mac OS X up until version 10.11
Please note the installation instructions and hints available on their site.