most keyboards support midi and there are different options with this on keyboards. There is midi in, midi out, and also there can be midi thru.
Midi-in...lets a pc play back through the KB.
Midi-out..lets a KB play into the pc to record.
Midi-thru.daisy chains more keyboards/drum maching etc.
You will just need a midi adaptor which goes from the KB to the joystick port on the pc. There is a lot of software (even freeware) to do complicated midi tasks.
The more midi channels the keyboard has the better, this is how many seperate instruments the keyboard can hear from the computer. Also , I think its called polyphonics, how many notes an instrument can play at once for chords etc.