function creaAjax(){
  var objetoAjax=false;
  try {
   objetoAjax = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (e) {
   try {
     objetoAjax = new ActiveXObject("Microsoft.XMLHTTP");
     } 
     catch (E) {
     objetoAjax = false;
   }
  }
  if (!objetoAjax && typeof XMLHttpRequest!='undefined') {
   objetoAjax = new XMLHttpRequest();
  }
  return objetoAjax;
}

 function FAjax (url,capa,valores,metodo)
{
   var ajax=creaAjax();
   var capaContenedora = document.getElementById(capa);
	 if(metodo.toUpperCase()=='POST'){
		ajax.open ('POST', url, true);
		ajax.onreadystatechange = function() {
			 if (ajax.readyState==1) {
					 capaContenedora.innerHTML="Loading.......";
			 }
			 else if (ajax.readyState==4){
				if(ajax.status==200)
				{
					 document.getElementById(capa).innerHTML=ajax.responseText;
				}
				else if(ajax.status==404)
					 {
						 capaContenedora.innerHTML = "La direccion existe";
					 }
				 else
					 {
						 capaContenedora.innerHTML = "Error: ".ajax.status;
					 }
			}
		}
		ajax.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
		ajax.send(valores);
		return;
	}
}