Digital Cable TV tuner

Yes there is, but the minions like you and me can't get one -- yet. The cable companies own them and license them out (to companies like TIVO). If and when they do become available to the general public, they will still (probably) be owned by the cable voles, and to get one, you'll have to rent it from them. The only current option is to take the analog feed from your digital cable channel box and input it through a capture card, like a TV tuner or your GPU if it has capture. The other option is to get an HD TV Tuner card and capture the signal over the air (OTA), but in order to do that, you have to be pretty close to where the cable company picks up its feed. How many channels you get is a function of how close you are to that locale.