I know this is not exactly what you asked but it may be relevant.
We have a 53-inch projection TV that is HD-ready, meaning it needs a cable box. All the stations filled the screen, but DVD's depended on whether we bought letterbox format of not. They either filled the screen or had black bars at the top and bottom.
However, we recently got the cable box for HD and it presents some interesting challenges. There are several ways to set it up. Full HD is 1080 but the installer set it up for 720. The HD channels as well as the non-HD channels still fill the screen but the HD channels have the sides cut off - meaning some text is not showing. I went to the controller and changed to full HD - 1080 - which makes all the HD channels appear in letterbox format, and the picture is awesome. But the non-HD channels have black bars on the top and bottom and on both sides. And my husband insists that he can't see the HD channels as well with the widescreen format and he thinks he's being cheated out of something with the non-HD channels.
This big TV, although being only 6 years old, has a problem. It won't come back on when it's cold without a great deal of trouble pushing buttons, and having the lights flicker when the TV is trying to come on. So pretty soon we will have to get a new TV and they don't sell the big square ones any more. I don't know how long it will last being left on all the time; we jsut turn it to one of the auxillary inputs that has nothing coming into it.
BTW, the HD box came with an HDMI cable and it looks more like a computer connector than a TV cable; is flat and has about 5 plugs on the end. It uses auxillary 4 on the TV and the VCR is still plugged in with the round cable and still works on channel 3.