Your DVDs will not look better on a HD tv unless your DVD player is progressive scan. If it doe not have that, they they will look the same.
Also, you cable and broadcast stations will also look the same. Unless your HD tv has the built in ability to render the pictures better. That is not always built in.
I have a nive HDtv, Sony Wega. I had the HD package from Dish network for a while, it was not worth it. I got rid of it. The only HD I use it with now is from my XBox 360. For that, it looks great.
We were considering getting one, but after we looked into it we really see no point.
I mean only SOME channels are in HD SOME of the time. And they aren't even good channels...
Is there any other reason to get an HD TV? I know the 360 is and the PS3 will be... but I dont like 360 and PS3 isnt out yet.
Also, all DVDs are in 640x480 right? That must look even worse on an HD LCD then it does on a regular SD TV. Did they pick a winner yet in the Blu Ray vs. HD DVD? I mean, after one of those starts comeing out, I can see why people really would start wanting an HD TV.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic