Hi Mick.
I'm not very computer savvy so I don't know if you can use computer parts to run a stepper motor, but I know how to make a set-up using the proper parts.
For a smooth tracking system you will need a 1.8 degree motor, not the more common 7.5 degree motor. The 7.5 give more of a jerky motion.
You will also need a Stepper interface module. Jaycar sell them at a reasonable price at around $50.
Jaycar also has the software for free to drive the stepper interface and motor
At this page link you can see the link to the free software (AA-0352 Software.zip) at the bottom of the ad for the interface:
http://www.jaycar.com.au/productView...Max=&SUBCATID=