Hey I'm not a CNC DIY but i thought this could help. Awhile back i needed to control a stepper motor. So i found this circuit. It'll take some implementing to get it to work right, but it's a good start!

http://www.aaroncake.net/circuits/stepper.asp

That driver will not drive larger amp steppers, Most people choose to buy the HobbyCNC Kit or build their own if you want to DIY.

This is the most popular site people use.

http://pminmo.com/

Joe