Last Summer I was experimenting with using a Windows 7 machine as a home theater PC and ran into an issue I thought was obsolete - overscan.
Overscan goes back to the days of CRT TVs where the edges of the image are cropped off by the bezel of the TV so the picture completely fills the part of the picture tube that you see. I thought that it was an obsolete concept with the advent of HDTVs. So imagine my surprise when I hooked up the computer to my Samsung 46" LCD HDTV and found the icons on the left edge of the screen were clipped off as well as the task bar. It turns out that even though the physical resolution of the LCD panel is 1280x1080 the TV was stretching the pixels to clip off some to accomplish the overscan.
You'll get the best picture no matter what the source if the resolution of the signal exactly matches the resolution of the LCD with no pixel scaling required. Well it turns out when overscan is being used in your TV you'll get scaling even though you're feeding a 1080P TV with a 1080P source like a Blu-Ray player, Xbox 360 or Sony Playstation gaming console, or home theater PC. In the case of the PC it was even more annoying because critical parts of the user interface were clipped off the screen.
By far the first choice is to see if your TV has a mode which eliminates the overscan. In the case of Samsung TV's this mode is called "Just Pixel" mode which is found in the p-size settings button of their newer model TVs.
If the device you are playing from is a Blu-Ray player or a game console then you can just live with it - the user interfaces of those devices don't depend on elements near the edge of the screen. You just won't be getting quite the picture sharpness possible in HTDV because of the pixel scaling.
Windows does not normally have overscan compensation settings for displays, but depending on which video chipset has you may be in luck. One disappointment here was Intel onboard graphics - despite the fact that Intel has motherboards which are intended to be used in home theater PCs, as of the Summer of 2009 the Intel graphics drivers did not have settings to compensate for overscan. I believe that at least one of ATI or NVidia did have settings for this - you're shrinking the Windows desktop size by the amount of the overscan so that the entire desktop will be visible, but this means you won't get the full sharpness of 1080P.
Believe it or not there is an unofficial firmware available for certain Samsung TVs which did not come with a "Just Pixel" mode which add this feature! As it happens my TV (model# LN-S46960) was one of them and I was brave/stupid enough to try this firmware and it worked! Before the firmware my TV had "16x9", "4x3" and "Wide Fit" modes when I pressed the "P-Size" button on the remote, but now when I'm viewing a 1080P source via HDMI I also get a "Just Scan" option, and that's the mode which does not have overscan. For more info check this thread on AVS Forum. Keep in mind that this really could brick your TV and Samsung would probably tell you you're out of luck, and you should feel REALLY comfortable with following technical directions before you even consider doing this. I was feeling really brave (and frustrated) that day, gave it a shot, and was happy with the results - your mileage could very well be different and nobody (especially me) can be held be responsible if you brick your TV.