Synchronized videos with superimposition

[Thierry]

Hi,

I'm in the process of making some animated slides
with RevStudio for a talk
I'm doing soon in Paris.

1) I have to my disposal 3 videos ( .mov ).
2) I'm really dummy with video stuff
3) I'm on a MacBook/Tiger.

  I would like to  have one in the background,
let say , half screen , and the others two, much smaller in size
( 15% each of the first ), superimposed on the first.

I managed to play them all together ,
but can't do the superposition ( flashing at the intersection ).

Then, with iMOvie HD tried to build one Video out of the 3,
but there is only one video track :-(

Any enlightment are very much welcome.

Regards,
Thierry