HD to my tuner

I have a ATI 650 dual pci express tuner. It has an HD tuner built into the card, but the only ports it has are two F-Type standard coaxial connectors and an S-Video connector. If I had HD tv service such as Dish Network or DirecTV how do I get the HD to my computer? I know that coax is very capable of transporting the signal, but very rarely will an HD receiver have a coax output. I have an S-Video to component converter, but that was designed to connect my video cards output to a component input of another device. S-Video isn't high def from what I've read. I assume that the best picture that I'd get would be 1080i so how do I get that from the set top box into my computer?