if (document.images) {

  img_nav_sub4_1on = new Image();
  img_nav_sub4_1on.src = "../_img/nav_sub4_1over.gif";
  img_nav_sub4_2on = new Image();
  img_nav_sub4_2on.src = "../_img/nav_sub4_2over.gif"; 
  
  img_nav_sub4_1off = new Image();
  img_nav_sub4_1off.src = "../_img/nav_sub4_1off.gif";
  img_nav_sub4_2off = new Image();
  img_nav_sub4_2off.src = "../_img/nav_sub4_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");
    }
  }
}