I finally managed to put everything together: the Arduino, the Ardumoto and the RP5 platform. It was like plug&play. But as can be seen in the movie, it lacks "intelligence". The next step is to give it the "power of sight".
After some search I came across this rather simple but sufficient chassis from Pololu. It already comes with 2 DC motors. Seams to be exactly what I need to try the Arduino and the Ardumoto.