If you have only one set of inputs on the TV, you'll need an external switcher. I have a Sima SVS-4 and love it. They have a newer model, the SVS-4D, that should be the same thing plus digital audio. It auto-switches inputs. In your case, that means that you'd leave the DVD player off until you wanted to watch something on it. When you power it up, it'll autmoatically switch to the DVD input. When you cut it off, it'll switch back.

Mine was only $100 when I got it, but they seem to be more expensive now.