AFAIK VGA is as high on PQ as component or HDMI.
I've lost track of which of the three is HDCP compliant though. I think component is the only one that isn't...?
Doesn't affect me, I don't have the 360 HD-DVD addon nor do I plan on getting a hi def DVD format anytime soon.
VGA is just as high true, sometimes better than component even.
HDMI is the 'only' one that can carry HDCP as it is digital, though it makes zero difference for the HD-DVD player as the films unlike BluRay do not have HDCP on them and neither are they region protected.