My guess is you have your aspect ratio on your tv set to something other than 16:9. My dad has a Hitachi plasma 16:9 television above his fireplace mantel. Many of the channels on cable are not in 16:9 format, but standard 4:3. So he gets black bars on the sides, he does not like that...So he uses some weird setting called 4:3 zoom or something like that which gives him the same thing you describe along the bottom of the screen. If he cycles through the various aspect ratios on the remote control and selects 16:9 standard it looks fine.
