Hi, I'm in the same phase as you I believe so it would be interesting to share some experiences as we gain them. Yesterday I assembled my new (to be) htpc with a Gainward 6600gt on an Asus P5AD2-E Premium motherboard. I chose the nvidia graphics board because my old 4600 board in my old htpc worked so well with my Sony HS-10 projector and I assumed the driver would be the same (well, it wasn't...).
With the old htpc, using VGA, I get a brilliant pic with 1368 x 768 pixels but @ a no-good 56 Hz. Using the 720p res through a 5 m DVI cable i get my coveted 50 Hz. The problem with the 720p is that the pic gets cropped. Showing the Windows desktop you lose almost all of the taskbar at the bottom. This is a well-know problem with at least some older Sony projectors. So basically you have a choice between two evils: the pan-judder of the 56 Hz VGA or the cropping of the DVI. I chose the latter.
With the new system, I have so far tried the DVI output, now through a 10 m cable. The colors looked like an LSD trip gone bad. Maybe the cable is too long or of poor quality. I then tried the component output of the 6600gt @ 720p which worked fine except when I play a DVD I see everything but the movie. There's just a black rectangle where the Return of the King should be playing. Doesn't matter if I set the projector as the primary screen or not. I've tried both the nvida and the windvd codecs. @ 576p I managed to get a picture (still through component). When I quit yesterday the WMP still insisted on showing the movie on both the LCD display *and* the projector, with judder on one of them. But today's an other day...
What is the native res of your projector. What output from the graphics board are you using?
It seems to me that the 6600gt features were just added to the last official version of the driver and may thus not be mature as of yet. So don't throw out the pc. Or if you do, pls throw it in my back yard!
Pls tell how everything progresses!
-A