Better look at the hardware side first - what kind of steppers? 4 wire, 5 wire? 4 wire are bipolar and those with more wires are generally unipolar. Each has its own set of benefits and problems. A bipolar stepper will require 2 H-Bridges to operate. and Unipolar will need 4 transistors - depending on current either NPN or MOSFETs.
There are several folks who have done some work with CNC plotters/routers/mills. Might look up what some of them have done.
I have done some work using first the Arduino and then an ATtiny2313 as the logic for a stepper driver - they take Step/Direction inputs and supply 4 control signals to the 4 transistors for an unipolar stepper drive. Here's the link - http://arduino.cc/forum/index.php/topic,84809.0.html