PT44LCX65 - Panasonic Rear Projection

I just went up to best buy to buy a HDMI cable so that I could receive the free HD channels that I can get through Timewarner cable, and I get home, hook it up and it's the same thing. I'm just getting the standard non-HD picture that has gray bars around it. How can I get HD? Is it a setting on my TV? A setting on the digital box?? The digital box is a Scientific Atlanta Explorer 8300HD.