function preloadPenguin() {
  if (document.images)
  {
    peng1 = new Image(150,150);
    peng1.src = "Penguin.jpg";

    peng2 = new Image(150,150);
    peng2.src = "Hamburger.jpg";

  }
}

function over_image() {
  if (document.images) {
    document["PengImg"].src = peng2.src
  }
}

function out_image() {
  if (document.images) {
    document["PengImg"].src = peng1.src
  }
}


window.onload = preloadPenguin;