tony,
You're welcome.. actually I'd figured out the math some time ago for my own... just plugged your numbers in...
For more info on stepper motor techniques there's a great tutorial at
http://www.cs.uiowa.edu/~jones/step/index.html but yes, the idea of micorstepping is to interpolate between the natural steps of the motor, which is commonly 200 (1.8degrees) although other types exist.
If you want to ensure the rails are mounted on something level, consider self-levelling epoxy - there are several threads on the Zone about it.
"scrap breast imaging... couple of lead screws in it for lifting the breasts up and down" the mind boggles
