Last time I took the fight, I didn't find any way, not even a clue, on how to turn on the TV-out with mesa drivers. Physically it should be possible but I'm not sure if it works out. After several months I finally gave up and installed the proprietary fglrx drivers from ATI, after which TV-out worked except that it messed up the pc monitor's gamma settings always when fglrx driver was used (this is probably a 'bug' in some cards, but not in every one of them).
If TV-out is a necessity, you'll save a lot of time and energy if you just go ahead and install the fglrx drivers from ATI. It's not a click-and-go process, not often at least, but definitely works better than Mesa at the moment if you want TV-out and such things.