Just bought a 50' plasma -- DVD picture seems fuzzy...

I just bought this Panasonic plasma TV for about $1000: http://www2.panasonic.com/consumer-electronics/support/Televisions/VIE RA-Flat-Panel-HDTVs/How-To-Guides/model.TC-P50S2.H#ts

I rented Clash of the Titans, thinking that movie would have some special effects that would allow me to judge my new TV's picture quality. However, I was not entirely pleased with the picture I saw on the screen. Now unfortunately, my means of playing DVDs are probably not ideal. I played Clash (1) on my Xbox 360 with component cables, (2) on my Xbox 360 with an HDMI cable, and (3) through my laptop attached to the TV via an HDMI cable. None of these really had the picture I was looking for. What's wrong with the picture, exactly? Well, there's a fuzziness to it. It does not have the crispness that I was hoping to see; in fact it's less clear than the picture on a tube TV would be. This is how the TV looked at the store too, but the worker there said that that was because their "feed" was terrible. Should my DVDs look this way? Did I overestimate the picture I would be getting? Do I need to hook up a different DVD player, or maybe do I need to just stick to Blu-Rays now? (I have nothing to play Blu-rays with at the moment, so I can't test that theory.) Or maybe the settings on my TV need adjusting. I know that the Xbox is set to 1080p.

All this is very foreign to me. I will say this: the video games I have run, on the same Xbox that was playing the Clash DVD, look perfect. Thanks for all your help with the DVD issue.