image1on = new Image();
  image1on.src = "images/nav-full1.gif";
  image2on = new Image();
  image2on.src = "images/nav-full2.gif";
  image3on = new Image();
  image3on.src = "images/nav-full3.gif";
  image4on = new Image();
  image4on.src = "images/nav-full4.gif";
  image5on = new Image();
  image5on.src = "images/nav-full5.gif";

function turnOn(image1,imageName) {
  if (document.images) {
    document[image1].src = eval(imageName + '.src');
  }
}
function turnOff(imageName) {
  if (document.images) {
    document[imageName].src = "images/nav-full.gif";
  }
}