Bad Picture Quality On New Toshiba REGZA 52HL167 52-Inch 1080p LCD HDTV?

I of late decided to buy a 1080p LCD HDTV, at the store the picture was fine and quite nice, but when I hooked it up to my digital cable box it looked very jagged and blurry, I have Comcast and it worked fine on my other CRT Tvs. I am using S-Video Component Cables to hook it up although it is still a terrible picture downgrade from what it was in the store. Any suggestions? Then am I able to just get an HD box without buying the HD service or will I need to pay a monthly fee to get a good picture?