if (document.images) {
  nav_home = new Image();
  nav_home.src = "images/nav_home.gif";
  nav_home_on = new Image();
  nav_home_on.src = "images/nav_home_on.gif";

  nav_about = new Image();
  nav_about.src = "images/nav_about.gif";
  nav_about_on = new Image();
  nav_about_on.src = "images/nav_about_on.gif";

  nav_ps = new Image();
  nav_ps.src = "images/nav_ps.gif";
  nav_ps_on = new Image();
  nav_ps_on.src = "images/nav_ps_on.gif";

  nav_location = new Image();
  nav_location.src = "images/nav_location.gif";
  nav_location_on = new Image();
  nav_location_on.src = "images/nav_location_on.gif";

  nav_contact = new Image();
  nav_contact.src = "images/nav_contact.gif";
  nav_contact_on = new Image();
  nav_contact_on.src = "images/nav_contact_on.gif";
}
function imgOff(imgName) {
  if (document.images) {
    document.images[imgName].src = eval(imgName + ".src");
  }
}
function imgOn(imgName) {
  if (document.images) {
    document.images[imgName].src = eval(imgName + "_on.src");
  }
}