Have you tried using the THX optimiser to set up your tv properly? Basically a series of test cards that you can use to adjust all you picture settings,contrast,brightness etc... You can find this on star wars dvd's and some others like Pixar films for example.
The factory settings on most tv's are miles off, and setting up properly makes a huge difference to the picture quality. You can of course pay for an ISF engineer to come round your house but will cost you a few £'s.
You also might need to set up the tv for day time and night time viewing as well. On my Pany plasma I set up the "cinema" mode on the tv at night time with the lights turned off. And then set up "eco" mode in normal daylight conditions for daytime viewing.
Also the quality of various dvd's,tv programs etc can vary hugely. If it's a poor quality recording to begin with then there's not alot that can be done to make them look good. Just compare ITV to say BBC1 on sky for example.
Im not sure if your tv is "isf calibration enabled" but if it is there's probably more options than you can shake a stick at. Which could make setting it up properly more tricky. Maybe any owners out there could help you out with their settings, could be a good base to work from.
EDIT: have a look at his as well http://whathifi.com/blogs/television/archive/2007/09/17/how-to-boost-your-tv-s-performance.aspx