It's like connect the DVD to your TV and you're in business, right?
The whole idea of home theater is to recreate that great theater experience minus the preshow ads, the tall guy in front of you, and the $10 popcorn.
So unless you have the most amazing TV speakers ever made, you're gonna need more than at TV and a DVD to give you great sound to go with your great HDTV picture.
Today's HDTVs can produce stunning pictures, with lifelike color and detail. But when it comes to big, convincing sound, not so much. That's why you need a separate sound system to provide realistic, engaging audio effects that can match the quality of those pretty pictures.
Your home theater doesn't have to be fancy, complicated, or hideously expensive. You've got plenty of options for getting good sound, from simple one-speaker systems to more channels than first generation TVs had. You'll be looking for something that fits your room, your budget, and your taste.