What Video card to buy?

[Buzz66]

Okay, I am new to this so please bare with me. My question is what video card should I buy with my type connections. I use Comcast cable with their DVR box (needed to recieve HD from them). So the coax cable comes out of the wall to the DVR box; then out of the box with a HDMI cable to the TV. I was think of connecting it with the coax coming out of the wall going to the GBPVR box, out of the GBPVR box to the Comcast box and then HDMI out of the Comcast box to the TV. So what video card would be able to do this?

Thanks