Chances are, no. If you want a better signal just buy component cables.
People with good quality television sets aren't worried about 480P. Any progressive signal looks great with a good TV. Still, I think Nintendo are hiding 576P ... in theory Wii should be capable of this. Chances are we might get it in a firmware update for when the "DVD Wii" is released.
Edit 1: Spelling and grammar corrections.
Edit 2: Too many people are getting mislead with my post.