Connecting a laptop to my old projector

Hello all,
I'm having a problem with my Panasonic video projector model PT-102N.
It's an old model, and I want to connect my laptop to it. So I connected the
display-connector of the laptop to the RGB-connectors of the beamer, but I
get a very trembling image out of the projector. It looks like the
synchronisation is not right. I tried setting the resolution of the laptop
screen to 800 x 600, but this did not solve the problem.
When I connect a videoprojector to the video-connector, everything works
fine.
Anybody an idea how to solve this?
thanks in advance,
Theo