Good open source tv card software

Hi,
I don’t know if you can help me but ill give it a shot. Do you know any open source software that I can use to see good picture quality from a tv card (im not recording just watching tv)?

I am trying to develop a software that one of its functions is watching tv (no recording just watching). I am developing the software in .net and it is going to run on a pc with win xp. The problem is that no matter what tv card I use I cant reach the same picture quality as the quality of the tv card's software. And I cant use the tv card's software so… I don’t know what to do. I am using the leadtek winfast tv card at the moment, I have tried to contact the manufactor for development tools but nobody could help me. I have tried using several libraries for video display, including OpenCV, Viscom Video Capture ActiveX and a .NET library. But the picture quality is till poor…
What am I doing wrong? 
Im sure there is a very simple solution I mean there are thousands of software out there that use tv cards but I am stuck!!!!! Please help!!!!!
Thanks in advance…
"Not4sale"