Windows XP has a MIDI port limit, which is higher than 98 or 2000, but if you have had failed MIDI interface installations, your computer could have more than the allowed MIDI ports installed and this will cause the latest ones not to show up. Midiman/M-Audio has a utility which will clean out your MIDI ports. Go to www.midiman.com and go to drivers. Choose any of the Midisport series and Windows XP, then download MidiFixUtil. Run it and it should clean out your MIDI ports.