A lot of LCD flat panel HDTVs also overscan the video they receive over HDMI/DVI or component since they do this in order to emulate a standard CRT TV which have overscanned the video inputs for the last 50 years. Overscan is actually a benefit for TV and DVD programs since they all assume that image will be overscanned and therfore they put no meaningfull content near the edges of the video. Therfore the meanignfull content is larger on the screen.
The problem comes if you are going to use an HDTV and a PC monitor since PC desktop applications put lots of meaningfull content such as the task bar on the edges of the display.
So if you are going to use an HDTV as PC monitor you want to be sure that the unit has a VGA (PC) input available if the HDTV does not have the ability to disable overscan over HDMI/DVI/Component
The reason that you adjust for the overscan by applying overscan compensation in the PC card driver is to get the appearance of 1:1 pixel mapping which you don't get when the overscan zooms in on the picture 6-8%.