i plan on playing the break in DVD for my new 50px75u - i dont yet own a up-converting dvd player - can i acheive the desired results using an older progressive scan dvd player, or do i need to use a newer up-coverting dvd player to break this puppy in?

Any DVD player will work fine. The break-in DVD just sends full-screen color images to the plasma, so upconverting has nothing to do with it.