function objetoAjax(){
	var xmlhttp=false;
	try {
		xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
		try {
		   xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
		} catch (E) {
			xmlhttp = false;
  		}
	}

	if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
		xmlhttp = new XMLHttpRequest();
	}
	return xmlhttp;
}

function SwitchMonth(url){

 divContenido = document.getElementById('calendario');
 
 ajax=objetoAjax();
 ajax.open("GET", "ax_calendario.php?"+url);
 ajax.onreadystatechange=function() {
  if (ajax.readyState==4) {
   divContenido.innerHTML = ajax.responseText
  }
 }
 ajax.send(null)
}