A lot of the fixed pixel HDTVs will add approximately 5% overscan to the incoming signal to push the edges of the picture beyond the display limits. Many of the newer sets have a feature to turn the overscan off especially for computer applications.
The problem with overscan is it is added by use of the sets scaler. In your case the 1280x720 input signal is not just scaled to 1366x768, but something even larger, say about 1400x800 and then the center 1366x768 area is what winds up on your screen. Definitely not 1:1 pixel ratio. That is what causes the fuzzy text and blurry picture. Normally this won't have anything to do with the color or other elements of the picture though.
HDTVs that are only expecting a HDTV video source at their inputs are problematic to hook up to a computer and many people use powerstrip to fiddle with the resolution and timing to set up a resolution within a resolution so the resulting image sent to the HDTV ends up at a 1:1 pixel resolution. nVIDIA drivers had the ability to set this also, but as far as I know ATI never has. powerstrip set up is very tricky and is not possible for me to tell you how to set it up for your HDTV, unfortunately, as it takes trial and error.
That's why I stress to our customers that if you are going to use your HDTV with a PC, be sure to get one that plays nice with a PC.
There is not any technical reason why your PC (VGA) input should not look just as good as your HDMI input assuming the HDTV is calibrated properly and you have a decent video card. The only possible variance would be the resolutions supported could be different on the VGA input. If the colors are different, then the white balance is probably not calibrated to near 6500k for the VGA input.
I don't have any specific thing to tell you to try, but hopefully this will give you some areas to look into.
Last edited by rbinck; 04-11-2008 at 09:52 AM..