PiStep

4Tronix do a small stepper motor board driver that lets you connect 2 (or 4 steppers depending on model) to your Pi.

The normal ScratchGPIO stepper commands can be used http://simplesi.net/scratchgpio/using-stepper-motors/

Basically, create variables called MotorA and MotorB and then issue

broadcast stepper

You can then vary the values of MotorA and MotorB from -100 to 100 to control the speed and direction of your steppers