function preload_images() {
  var imgslist = new Array(
    "images/menu_demo.gif",
    "images/menu_demo_hover.gif",
    "images/menu_services.gif",
    "images/menu_services_hover.gif",
    "images/menu_portefolio.gif",
    "images/menu_portefolio_hover.gif",
    "images/menu_contact.gif",
    "images/menu_contact_hover.gif");

  var imgs = new Array();
  if (document.images) {
    for (x = 0; x < imgslist.length; x++) {
      imgs[x] = new Image();
      imgs[x].src = imgslist[x];
    }
  }
}