Hi,
I have written a library for the motor control:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1280519240
I will upload it to the playground if people think it is useful and want to use it.
Cheers.
BTW: JoakimCh, I've seen you video on facebook.
I am actually doing exactly the same, only my car is controlled using a nordic module (from sparkfun) and a GamePad 