Below is a spreadsheet I've created to help with drive design. It supports both steppers and servos, allowing you to enter component parameters (motor voltage/current/inductance, drive reduction components, screw type, etc.) and it calculates such things as optimum supply voltage for steppers, overall reduction ratio, step size, steps/unit, axis thrust, required step rates, etc.
At this point, I can't guarantee it's 100% complete or correct, but it is to the best of my knowledge. If you find any problems, or see anything that should be added, please let me know.
Regards,
Ray L.
Updated spreadsheet 10/27/2009 12:15 PST to correct errors in metric conversion, and thrust calculations.