You are probably running your TV-Out at 50Hz PAL standard instead of 60Hz NTSC standard (if you're in American, vice versa if you're in Europe). That is exactly what you would expect to see under those conditions. You can change mode in the driver.
Unfortunately you're probably not even wanting to hear that, so go buy your AGP8x card, it will most likely work, they are backwards compatable.
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>