[necropimp]

a few suggestions... use a different input on the TV for the Wii... go through all your component inputs then s-video then composite

try third party cables (if the problem improves or gets worse either way it will determine if the cable is part of the problem)

does your receiver have component switching? if so try a running the video through the receiver (you never know..) if it can send the video from the component to your tv through HDMI do that