OK, I found a card and hooked it up and it produces great video quality through an S-Video port.

However, there's a problem. If I leave the TV on for a while (anywhere from a few seconds to 10 minutes or so) the video will eventually start blinking back and forth between a color and b&w image, slowly at first, and then rapidly. Once this starts, the only way to stop it is to turn the TV off and back on.
I've tried the three different S-Video inputs on this TV and they all have the same problem. I don't have another TV with S-Video inputs to try however.
Interestingly, if I go into the TV's menu mode (which displays the video signal in a smaller window so you can see the input image and the menus) the problem completely disappears and the video in the window looks normal (although smaller of course because it's in a window).
Any ideas?