circuit design for stepper motor driver

I am looking for a fairly simple circuit that can drive a small (12 volt, 400mA) stepper motor at a specific constant speed. This is for a timekeeping/clock application, so accurate timing is essential. The circuit must also incorporate a momentary switch which will run the motor at a higher rate of speed, for setting the clock. A directional control would be welcomed as well. Power supply is up to the designer, but something in the 6~12 VDC range would be preferred. This would be a low-volume project, starting with 10 units, after confirming that a prototype is acceptable.