if (document.images) {

  img_nav_sub7_1on = new Image();
  img_nav_sub7_1on.src = "../_images/nav_sub7_1over.gif";
  img_nav_sub7_2on = new Image();
  img_nav_sub7_2on.src = "../_images/nav_sub7_2over.gif"; 
  
  img_nav_sub7_1off = new Image();
  img_nav_sub7_1off.src = "../_images/nav_sub7_1off.gif";
  img_nav_sub7_2off = new Image();
  img_nav_sub7_2off.src = "../_images/nav_sub7_2off.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");
    }
  }
}