Hey Kane;
You'll need a serial port based Midi interface. Check Mark of the Unicorn for interface. I have an old one that is still decent. You might find one online at eBay or even here. They should be cheap. Then you're in business.
As for the USB and Firewire situation, you can use SCSI external Zip drives or Hard drives. If so, then you can use, MPCProgramMaker. That will make your MPC sound library use happier. For info on the scsi drives and so on, check out Mac Addict. There are lots of dealers who still sell these things around.
Peace.
Homershines