You may be seeing only the difference between standard definition (all DVD's) and HDTV in which case you don't need to buy anything.
Yes there are a few DVD players that output digital video, but before you buy one of them, see if you can borrow or even rent a DVD player with its own (analog red, green, and blue) component video jacks.
So-called progressive scan players output either 480i or 480p from the same output jacks. Almost all HDTV's accept both although the TV may have separate component video jack triplets for 480i and 480p. Try both. A rented player might not construct the best 480p from the native 480i of DVD. Should you find that a non-progressive player with component output improves things drastically from what you have now, you don't have to go furhter to investigate players with digital output.
If you are not satisfied with what you got from a non-progressive DVD player, shopping for progressive scan needs research and time. All but the oldeest HDTV's convert all standard definition input to progressive scan if the input was not already progressive such as from a progressive DVD player. You need to do the research to learn what is a good job of making progressive scan. If the TV does a good job, you don't need a progressive DVD player. If the TV does a poor job you need to be careful not to buy a DVD player that also does a poor job.
Video hints:
http://members.aol.com/ajaynejr/viddoubl.htm
