A:
I am not using the HDMI connection, which has more to do with quality of signal than type of signal. If you can't use HDMI, use S-Video, then composite video. The coax "cable" video is a last resort. Sounds like you will have the same problem I do with some channels--a high def larger screen like this highlights a low def signal as a grainy picture, especially if you use the zoom feature.
My router is class N, which means I will get a faster loading speed (movie starts faster as it fills the buffer) and more picture bandwidth (better picture quality, or fewer movie delays to rebuffer the incoming signal). The B/G router will lose some picture quality, but so can nasty internet providers who see Netflix sucking down too much of their pipeline bandwidth already and limit the bandwidth for movie downloads. I can say that when we upgraded from class B/G to class N it was night and day and a lot cheaper than this TV. Worth every penny--especially if there are multiple users in the house doing other things at the same time.