Question about video card and videos

This is a small question that I came across just now when I was watching Pink Floyd Pulse... When I go full screen, there are like these squares, like blocks that are just from a low quality video set to full screen in 1280x960. Is this the video cards fault? Like why cant I watch it on the computer the same as on tv? The picture on the computer isnt as sharp as it is on a tv, even know I have a HD monitor.

I have a nvidia 6800GS oc'ed to 500/1200, and I just wanted to know if this was the cards fault.

When I get a gecube x1950xt, will that make a difference in the sharpness of the video?

Thanks