Hi-Res Monitor as a TV screen?

Can anyone offer advice on using a Dell 20" widescreen Ultrasharp monitor as a means of watching DVD's with a freestanding dvd player as the source? The Dell's image quality is as good as a Mac Cinema Display's (1680x1250), only it has more inputs. The Dell has s-video, DVI-D, and Composite inputs, so it will recieve a signal from my DVD player and play movies, but the resolution is not nearly what it could be. Connected to my computer it is close to HDTV quality. But connected directly to my Sony DVD player the image quality is like that of a low-res JPEG stretched across the screen.

The problem is I want to use the single monitor for both my computer monitor in my home office, and when watching movies, I'd like to use it in the living room connected directly to a DVD player - without the computer. (I don't watch TV so the inconvenience of moving my monitor for a movie is fine with me).

I think what I need is a tuner/processor of some sort, to process the signal in lieu of having it connected to my computer. Is this what hi-end video processors do? Would this work? (in theory only - I realize it would be costly) Are freestanding TV tuners available?

BTW, I'm not interested in buying another flat screen tv - I am after simplicity - less TV's in my life (and this world) the better.
I hope my descripition makes sense and I'd appreciate any input, bearing in mind I'm not after spending big bucks on this. My frivolous money stays in HiFi.