I was wondering if anyone could double check my code for running a stepper motor 12V at running at 60rpm. I used the format featured here: http://www.ladyada.net/make/mshield/use.html
My reading or your code is that you've got a 1.8 degree per step motor, that you want to turn through 180 degrees in half a second.
Is that what you wanted?
Caveat: I have never used this library.