function update_navigation() {
   try {
      var sel_item = nav_items[0];
      for ( var i=1; i < nav_items.length; i++) {
         var item = nav_items[i];
         if( document.location.href.indexOf( item.href ) > 0) {
            sel_item = item;
         }
      }
      Element.addClassName(sel_item.id, 'selected')
   }
   catch(doh) { /* alert('error: '+ doh.message || doh.description || doh) */ }
}