The black borders you see on your TV screen are caused by underscan from the TV encoder on your graphics card. Underscan occurs when a video signal does not reach the edges of your monitor and leaves a black border around the image.
Normal broadcast TV content is "overscanned," meaning the image bleeds/scans past the edges of the screen so it fills the entire monitor. PC CRT monitors usually will have a 1" border which is not viewable. LCD PC monitors are not overscanned.
Video cards compensate for this by creating a black border, which you don't see, to fill the border that is not visible. This black border appears on your TV. A feature called Resize Desktop in the NVIDIA Control Panel can compensate for this TV / HDTV limitation.