Picture size. I am using COMCAST HD service and my picture size on my Vizio 42in is way off, I can

Question

I am using COMCAST HD service and my picture size on my Vizio 42in is way off, I can not see half the heads on the people on the screen and if I am watching ESPN i can not see the ticker tape thing running across the bottom off the screen. Overall it seems as if the picture is out of size, I have adjusted all the zooms and picture sizes. What can I do or should I do?