if (document.images) {
  image1on = new Image();
  image1on.src = "images/tintuc_over.gif";

  image2on = new Image();
  image2on.src = "images/sanpham_over.gif";

  image3on = new Image();
  image3on.src = "images/ungdung_over.gif";

  image4on = new Image();
  image4on.src = "images/hotro_over.gif";

  image5on = new Image();
  image5on.src = "images/doitac_over.gif";

  image1off = new Image();
  image1off.src = "images/tintuc.gif";

  image2off = new Image();
  image2off.src = "images/sanpham.gif";

  image3off = new Image();
  image3off.src = "images/ungdung.gif";

  image4off = new Image();
  image4off.src = "images/hotro.gif";

  image5off = new Image();
  image5off.src = "images/doitac.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");
    }
  }
}