You cannot power a CDROM drive or hard drive from your MPC2000 or MPC2000XL. The power supply isn't built to support that kind of power draw. The reason you only see two wires is because the sampler is designed to use drives that only need 5 volts, like a floppy drive, zip drive or card reader drive. Don't damage your power supply trying to use a drive that the unit wasn't built to support.
You could run in a separate 12/5 volt power supply if you are dead-set on installing a hard drive internally. Those are easy to come by - in fact, I have hundreds of small power supplies that would do the trick. PM me if you need one.