You should read the thread: Overscan
Overscan is a function of your TV not the computer.
If you can get into the TV's service menus, you can sometimes reset the height and width to get rid of the overscan. All TVs are sent from the factory with the height and width set to overscan so you don't see the edge of the picture where there is usually video noise at the top and bottom. There is the possibility on some video cards to set up a "resolution within a resolution" but I don't think it is possible with your card. The result of this would be a reduced desktop resolution of something like 1100x700 for a 1280x720p resolution. I've read of this, but have never seen it.
All in all, HDTVs do not make good computer monitors. I use mine to watch video clips, slide shows, digital photo and as a video jukebox where I can size the window to match the screen. Being an old assembly language programmer, I learned to run the PC with the keyboard, so I dont need the whole desktop to show anyway. I located my desktop icons to have the ones I need when using the TV to be in the center of the screen.
Another suggestion for controlling the PC in your easy chair to allow you to sit across the room would be to use a laptop computer and PCAnywhere. Set your HTPC to be a host and then you can remote control it from your laptop. You need a fast wireless or hardwired network connection, but it works pretty well. Sometimes I use this for surfing where a group of people need to see the screen.
If you come up with any solutions to the overscan issue, be sure to come back and let us know how you solved it.
On the resolution of 1280x720 on boot up, I have an ATI 7500 pci video card with the latest Catylist drivers. I have powerstrip to be installed on bootup. My PC will boot to whatever resolution I select using the desktop properties. So if I set the resolution to 1280x720 before shutdown, it will boot up set to 1280x720. If you don't have the HDTV resolutions available in your desktop properties box, you may need to load the Catylist drivers if they will work with your card. I'm not knowledgeable of your particular video card. Also you might look into the use of the Omega Radeon drivers (you can Google to find them) if your card is a Radeon.