function go() {
   var index,param,href;

   index = document.catform.catmenu.selectedIndex;
   param = document.catform.catmenu.options[index].value;
   href = self.location.search
   if (href == "") {
      self.location.search="?tx_ttnews[cat]="+param
      alert(href);
   } else {
      href=href.replace(/\?tx_ttnews\[cat\]\=\d+/,'?tx_ttnews[cat]='+param);
      href=href.replace(/&tx_ttnews\[cat\]\=\d+/,'&tx_ttnews[cat]='+param);
      alert(href);
      self.location.search=href
   }

}