if (document.images) { 
  left = new PreloadImage('images/left_off.jpg');
  left_on = new PreloadImage('images/left_on.jpg');
  logo = new PreloadImage('images/logo_off.gif');
  logo_on = new PreloadImage('images/logo_on.gif');
  launch = new PreloadImage('images/launch_off.gif');
  launch_on = new PreloadImage('images/launch_on.gif');
}