You might be able to pickup a few channels, but for the vast majority of programming you would need a Comcast cablecard. Cable companies have slowly been encrypting more of their digital channels over the last couple years, and it's at the point where you would need a cablecard if you wish to access most of the content you would get with a cable box.
I suppose you could plug the cable box directly into the TV Tuner card, but you're still going to need a cable box and a long coaxial line.