function new_image(arg) {

  if (document.images) {
    rslt = new Image();
    rslt.src = arg;
    return rslt;
  }

}

function change_images() {

  if (document.images && (preload_flag == true)) {
    for (var i = 0; i < change_images.arguments.length; i += 2) {
      document[change_images.arguments[i]].src = change_images.arguments[i+1];
    }
  }

}

var preload_flag = false;

function preload_images() {

  if (document.images) {
    icon_home_over = new_image("images/icon_home_over.gif");
    icon_search_over = new_image("images/icon_search_over.gif");
    icon_contact_over = new_image("images/icon_contact_over.gif");
    icon_site_map_over = new_image("images/icon_site_map_over.gif");
    preload_flag = true;
  }

}