An answer to this would be nice indeed! I'm having the same problem, and I've looked everywhere too, without succes. In Windows on the very same computer (dual boot), it works like a charm, so it's not hardware.
In windows I use clone-mode too. The tv is my second monitor. When I open a mediaplayer, or any other player that uses overlay to play the video, then the tv shows this overlay full-screen. Another example: in Pinnacle studio (video editing), there's a small preview on the mail screen, but that window is shown full screen on the second monitor, which is VERY handy when doing this kind of work. I would love this feature in linux too!
(btw, I have a very simple geforce4 mx440)