My telly does have composite AV inputs, though - it's what the DVD is usually plugged into, and Apple do flog an adapter for that, too. So I bought one.
Not sure whether it's the tellyl or the cable, but it's not transmitting video, just sound. Interestingly, I've always had the DVD plugged in via both composite AV and a separate S-video cable - a setup I've had for so many years I don't remember setting it up. So it might be that the telly's just rubbish, and the video part of the composite socket is just plain broken.
Either way: Bah.