Fantastic Stepper Motor Tutorial from Open Design:

Stepper motor tutorial #1

An introduction to stepper motors. Answers to :
What are stepper motors? How are they constructed? What are they good for? How do I control them? Link: http://www.opend.co.za/tutorials/stepper.htm

Stepper motor tutorial #2
Stepper drive circuitry protection.
Common protection circuits and popular mistakes. Why not to use the most common circuit on the web. Link: http://www.opend.co.za/tutorials/steptut1.htm