function ajaxUpdateAgenda(agenda_select) {
 toDay = new Date();
 datumtijd = toDay.getTime();
 var xmlHttp;
 try {
   xmlHttp = new XMLHttpRequest();
 } catch (e) {
   try {
     xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
   } catch (e) {
     try {
       xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
     } catch (e) {
       alert("Your browser is old and does not have AJAX support!");
       return false;
     }
   }
 }
 xmlHttp.onreadystatechange = function() {
   if(xmlHttp.readyState == 4) {
     var responseText = xmlHttp.responseText;
     document.getElementById('kalender').innerHTML = responseText;
   }
 }

 var xmlParams = "";
 xmlParams = xmlParams + "agenda_select=" + agenda_select + "&";
 xmlParams = xmlParams + "datumtijd=" + datumtijd + "&";      

 xmlHttp.open("GET", "/content/inc_kalender.asp?" + xmlParams, true);
 xmlHttp.send(null);
}