i have a different model samsung that does the same thing. actually it is not a problem. hdtv is broadcast in 16x9 aspect ratio. what you are seeing is letterboxing. widescreen sets can adjust some programs so that they fit the screen without the bars. however some programs are broadcast in their origianl aspect ratio, commonly refered to as oar, and in those instances you will see black bars to maintain the original ratio.
I have a Samsung TXN3098WHF, my HD signal seems to be coming in fine, but in wide mode there are black bars on the top and bottom of the screen. Samsung says that the HD signal varies and will not always have a full screen picture. How can you have a HD picture with black bars? Anyone else have this problem? Thanks for the help.