Not often, there are a lot of people that complain about noise generated on DVI cables and poor image quality.
Hook your DVD player up via component and take a look at it.
ALSO: HDTV is a much better quality video signal than DVD video. No, I know your DVD player outputs 1080i or 720p - but the DVD video itself is NOT HD material. It is 480i material and has a much lower quality image than HD.
Try component cables.