the print screen will not work if you have direct 3d accelaretion set. You have to turn it off under your display adapter options and media player options... otherwise as someone mentioned before you can use powerdvd or other retail dvd player to do so.
Not that I update the site often but when I DO take screenshots for new releases I use VLC... Got it so I can just keep smacking F11 to dump full-res .jpg's out.