A friend just purchased a Samsung HLS-5088. There were several issues regarding overscan that had to be resolved.
First, his Nvidia 7800GS wanted to send a 1080i signal instead of a 1080p signal. It was very blury at 1080i. Once I got it switched to 1080p, the image became clearer.
Second, I turned on Cleartype in the appearance-effects section of the display properties (in Windows XP). This cleared up the text even more.
Third, I turned DNIe and overscan off in the service menu. With overscan on, there was about 5% overscan. With it off, there was still about 1-2% overscan with more horizontal overscan than vertical.
Finally, I used Nvidia's overscan adjustment to reduce the picture slightly. It still sends a 1080p signal, but the actual visible resolution is reduced slightly to fit the screen. It is a resolution within a resolution.
Because the horizontal overscan is greater than the vertical, the image still doesn't fill the screen perfectly. However, it is extremely sharp. In the video diplays forum there are instructions for using Powerstrip
to create the proper resolution within a resolution for the Samsung TV's. I plan to try that next. You may want to try those directions.