if (document.images) {

  image1on = new Image();
  image1on.src = "../img/navmain_1on.gif";
  image2on = new Image();
  image2on.src = "../img/navmain_2on.gif";
  image3on = new Image();
  image3on.src = "../img/navmain_3on.gif";
  image4on = new Image();
  image4on.src = "../img/navmain_4on.gif";

  image1off = new Image();
  image1off.src = "../img_fed/navmain_1off.gif";
  image2off = new Image();
  image2off.src = "../img_fed/navmain_2off.gif";
  image3off = new Image();
  image3off.src = "../img_fed/navmain_3off.gif";
  image4off = new Image();
  image4off.src = "../img_fed/navmain_4off.gif";

}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}