The dvi cable is said to be better on some tv's and not on others!
The larger the progection the worse the picture quality.
You should always notice a difference from hd to standard, butsome tv stations just bump up the picture to hd, while others actualy film with an hd camera.
btw cable cannot produce true hd due to the lack of bandwidth. Or digital for that matter. (i saw you have satellite)
I would try the dvi cable but if you buy a cheap cable you are losing video quality, Buy a good one. It may increase your pic quality by up to 7-10%
I assume you mean "the other cable" Component= red, blue, green. Also if your using the one that came with your satellite, thats part of your problem. Also make sure your tv has dvi input. It may have to be 2001 or newer to have that option.(these are the only 2 cables to support hd)