Audio interface. If you don't have one, then you'll probably end up with a mono signal with a 1/4" to 3.5mm headphone cable to plug into the line in on you soundcard or onboard audio. Should be near the same port your speakers hook up.
Audio interface should be nothing more than the 1/4" off the MPC out to the 1/4" in on the interface. Then USB or Firewire depending on how your interface hooks to your computer.