If you've only got the speakers on your TV, you need to buy more speakers and possibly an amplifier. What make/model are your DVD player, TV and (if you have one) amplifier, and how many speakers do you have?
You will normally need a 5.1 capable DVD player (most of them!), amplifier (some set-ups combine the two) and 5 speakers + a sub-woofer for full-on 5.1 sound.