For a basic setup you will need a computer with a parallel port and Windows XP or 2000. A breakout board of some kind (PMDX122 etc) Stepper/servo motors, stepper/servo drives and a Power supply suitable for the stepper/servo drives..
Other things that are not essential but preferable even on a basic system are limit switches and E-Stop. Also best to have ballscrews rather than the leadscrews normally found on a manual lathe.
The size of the lathe will determine what exact hardware you will need.
Hood