I've got an nVidia 7300 GT hooked up to my PC right now by using an s-video cable with a composite adapter. When I configure it to use S-Video, I get a black and white picture on my screen. When I set it to composite, the screen flickers with color for a SECOND, and then it goes black. I've switched between PAL and NTSC, and I get nothin'. My TV should be NTSC, as I live in the states.
I've resorted to downgrading my video card. It would appear as though the port on my 7300GT is not marked "S-Video", but rather "Video Out", and so I am lead to believe that using it like I would an S-Video port will not work. Using my old card, I was able to switch back to composite, and recieve a color picture on my TV. I know this won't help most people, but it's something to consider.
What s-video adapter are you people using? I couldn't get my old ATI 8 pin s-video to RCA to work on my 8600 gt, so I had to make one out of a 4 pin s-video cable and a rca cable. Works great now.......here is the link to make your own s-video to composite. http://www.epanorama.net/circuits/svideo2cvideo.html You do not have to use a capacitor it might make the video look better, but I didn't feel like finding one and mine works great without it.