Samsung LN40A550 40-Inch 1080p LCD HDTV

I recently purchased the Samsung 40" LN40A550 To say the least I'm not impressed. The colors no matter how I set up aren't very vibrant. The picture quality is poor, even on high def. channels. I'm hooked into the local cable system through their cable box using the coaxial cable from the box to the set. Is there any advantage to using a HDMI cable? Am I doing something wrong? Is there a possibility the cable hd converter box is malfunctioning??
Any help will be deeply appreciated. I'm certain I will return this set if I cannot work this out.

This is our first flat panel tv, and we couldn't be happier. TV and DVD's are superb quality. Sound may be a bit weak, but we can always add a speaker system. Highly recommended.

I had this Samsung LCD TV for about month now and I absolutely love it.
The quality is great. I have Verizon Fios at home and all HD Channels come out great.
The delivery was really fast too, I received in 3 days.
I will definitely recommend buying Samsung LCD TV through Amazon.com to anyone I know.

The TV arrived promptly and the men unpacked it and set it up and tested it to see that it worked. I am very pleased with it so far. The glare I had with my old TV is gone or barely visible without me having to pull the drapes every afternoon. Thank you very much.

We are very happy with the picture but the sound quality is poor. We had to purchase a separate sound system