if (document.images) {
  image1on = new Image(); image1on.src = "images/bo_about.gif";
  image2on = new Image(); image2on.src = "images/bo_links.gif";
  image3on = new Image(); image3on.src = "images/bo_inquiries.gif";
  image4on = new Image(); image4on.src = "images/bo_home.gif";
  image5on = new Image(); image5on.src = "images/bo_sitemap.gif";

  image1off = new Image(); image1off.src = "images/b_about.gif";
  image2off = new Image(); image2off.src = "images/b_links.gif";
  image3off = new Image(); image3off.src = "images/b_inquiries.gif";
  image4off = new Image(); image4off.src = "images/b_home.gif";
  image5off = new Image(); image5off.src = "images/b_sitemap.gif";

}

function turnOn(imageName) {
  if (document.images) {
    document[imageName].src = eval(imageName + "on.src");
  }
}

function turnOff(imageName) {
  if (document.images) {
    document[imageName].src = eval(imageName + "off.src");
  }
}