I have a Radeon All-In-Wonder X800. I Just recently tried out its television viewing ability. On both cable and antenna i can only get garbled black and white images. I use Comcast cable (non digital)
Maybe it's the cable itself. Try a new one. I think you have some settings you tweak. It could also be bad signals... bad channels... I have a wintv t.v. tuner (in my sig) and it works fine. Uses cable... adelphia to be exact...