You need to add:
Option "ATOMTvOut" "True"
to the device section of your config, and even then, tv-out is still experimental and may or may not work. Unfortunately, r4xx and r5xx are the least supported at the moment.
That did the trick, but I saadly get a black screen... are there some tips on how to maby get it to work? Now, if I have the S-video connected as Xserver starts, my resolution becomes 800x600, wich is not so cool.