Grbl is free G-code interpreter software to use with an Arduino,
for CNC milling control.
A low cost "shield" is also available, which is a stepper driver...

http://makezine.com/2010/06/14/grbl-an-arduino-based-g-code-interp/

http://dank.bengler.no/-/page/show/5470_grbl?ref=checkpoint

http://makezine.com/arduino/grbl/

(I've never used it. I use Mach3)


- Brian