Regular DVD Movies converted for HD Flatscreen TVs?

Is there something that will convert my regular movie DVD’s so they will show in HD on my new HD Flatscreen TV? Or at least get them to show better? All my DVD Movies look like cr*p on my big flat screen. They look like the regular cable channels do. Is there some way to get them to look like they are on a HD Channel? There’s no way I’m going to replace all my DVD’s with Blu-ray disc. I already have a fortune spent on the dam* DVDs and I ain’t goin to buy them again! It was bad enough replacing the VHS tapes with DVDs, now they want us to replace those with Blu-ray. What are they going to replace those with?