Hi!
Im searching for ideas,hardware aswell as coding for making a cartesian robot (controlled in X,Y,Z axis). My idea on this stage is still rudimentary(3 servos,"maybe stepper motors would be better?")
I've got great news for you!
The RepRap project has published PCB's, wiring solutions, and everything you need for this around the Arduino. The firmware is also working (newly completed). It is focused on Stepper Motors, but the motor drivers are pretty flexible.
It is a Cartesian robot... actually there are two designs: One is an enclosed frame using pulley system ("Darwin") and the other is based off a CNC design ("McWire RepStrap") that uses 1" steel water pipes. There are provisions for optical end-stops, etc [all controlled by Arduino].
Info here on the electronics:
http://www.reprap.org/bin/view/Main/Generation2Electronics