Hi,
First and foremost, I must state that the HD add-on is killer times 10. I have King Kong, as well as a few others and have nothing but raves to say. I have been running everything via 1080i and the component cables. That said, I ran out today and got the 360 HD VGA adaptor to see what the differences might be as compared to my component outs. From what I've read, standard DVD's get the upconversion treatment only via VGA outs, and I wanted to see what that would look like. Also via the VGA cable, 1080p is possible, and ALLEGEDLY my projector will do that, but I'm not sure there either if somebody knows.
Having never used either a VGA out on the 360, or my RGB in on my Sony Cienza HS51a (8 months old), I'm not sure I'm doing something wrong here.

When booting up the 360 after installing the VGA cable, it gave me about 12 resolutions to pick from. Long gone were the display settings I was used to:480p, 1080i, etc. Many of these resolutions to me looked like 4:3 physically on the screen, even though widescreen mode was selected as the display type. I broke out my projector manual and it stated the maximum resolution for the VGA connection was 1280 by 720, so I chose that one. It at least went to a widescreen mode, but there was still about 3 inches to the right and left of the screen that were not filled in, which has never happened to me before with the standard components out and 1080i selected.
Then to make matters worse, I lost about 1/2 of the picture setting options on my Sony front projector because I was using the PC RGB in. This was explained in the manual that this would happen, but, I thought it was a real downer as I have the projector really tweaked out with Gammas, RCP, Black level adj., etc.
I could live with all of that so far, had the picture absolutely blown me away when I put King Kong on again. But, it was not to be. Yes, it still looked good, but nowhere near as good as via my regular component cable outputs did!!!!!! It looked rather washed out and the colors just did not "pop" like they did via component. I would say on absolute terms the pic was only about 75% as good via the VGA output.
The only thing I have not mentioned is that I did have to use a 10 foot Belkin SVGA extension to get up to my projector as it's ceiling mounted. It was of the $30 variety. I have no reason to believe that would be the root cause, but I did not try it without it as I think back to my experiment.
Does anyone have any advice or can tell if I'm doing something wrong here? If not, this HD VGA cable is going back!