"I take it you need a certain kind of sound card to run this feature on? (my laptop only has a headphone socket that my external speakers use)"
Yes. Some soundcards allow you to send a different signal to the front and rear sockets. Also some external audio interfaces (USB or Firewire) have a similar facility. Most DJs use a laptop with an external audio interface.
As to your other question - you can get control surfaces which are hardware devices to interface with a computer (so that you get real faders instead of using the mouse) or mixing desks - which take either audio out from a couple of mp3 players, or have usb ports to take memory sticks. This type need to be connected to powered speakers or a power amp and passive speakers.



