YOur problem is not the Tivo, cables, noise or dish. It is the terrible video processor built into all of the mass market TVs. The processor is the single most important part determining SD picture quality (although all elements are important).

The processor is responsible for translating a picture of different shape and resolution (much lower than the screen) to fill all of your HD screen. The cheaper the processor, the worse it damages the piture being fed to your HD screen.

The only alternatives that will make a signifigant improvment (although the other suggestions here are a good start) are these:
- Use an outboard video processor (like the DVDO or Lumagen units)
- watch more HD material where possible

Hope that helps.