Like what IceCold said, check to see what connections your TV has. I assume you're using the RCA cables that came in the box, and that might be the problem, as while it OK for small TVs, bigger screens like yours will probably make the difference much more apparent.
Generally, the path from best-to-worst goes Component Cables (Red, Green, Blue), S-Video (larger black plug), and RCA (Yellow). For a big screen like yours, Component would be generally the way to go, IMHO.
And ignore Wandering's advice.