I just made a new HTPC to go along with my Westinghouse TX 42".
For the OS, I installed Windows Vista 64bit Business Edition, also using the latest 162.22 WHQL drivers.
With a DVI-HDMI cable going from the 8800GTS to the HDMI input of the TV, set to 1920x1080, I get underscan of about 2 inches in a giant square.
(I will take a picture later).
My only solution now is to use the TV's overscan button.
What I really want is 1:1 pixel mapping to use the entire screen!
By the way, on my MacBook Pro (Radeon Mobility), and other PC with a ATI Radeon X850, it works perfectly fine for some reason.
For the heck of it, I tried hooking it up with a VGA cable, and Vista didn't see the TV being able to use 1920x1080 resolution.