Well, I haven't seen a DVD yet that defaults to the DTS soundtrack when started, so you'll definitely have to select it on the DVD menu. If your receiver has an auto detect mode, it will then pick up the DTS bitstream without any assistance, assuming that you have a digital coaxial or optical connection going between the player and the receiver. Make sure you're on the right input on your receiver and that you have assigned the input if necessary in your receiver menu. You may also have to set the DTS output on your DVD player to bitstream (once again if you have a coax or optical connection). If none of this helped you, post what equipment you are using and you'll get more specific help.
DTS soundtracks should still be on a burned copy unless you are using a program that cuts the extra soundtracks and extra features to conserve disc space. This is usually done to fit the movie on a single disc (the movie itself may also be compressed for the same reason). You aren't pirating movies are you? Naughty, naughty!!