function CreateHTTPXmlObject() {
  var xml_obj = false;
  if (window.XMLHttpRequest) { // Mozilla, Safari,...
     xml_obj = new XMLHttpRequest();
     if (xml_obj.overrideMimeType) {
        xml_obj.overrideMimeType('text/xml');
     }
  } else if (window.ActiveXObject) { // IE
     try {
        xml_obj = new ActiveXObject("Msxml2.XMLHTTP");
     } catch (e) {
        try {
           xml_obj = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e) {}
     }
  }
  if (!xml_obj) {
     alert('Cannot create XMLHTTP instance');
     return false;
  }
  return xml_obj;
}

function makeRequest(url, callbackfunction) { 
  //http_request = false;
  http_request = CreateHTTPXmlObject();

  http_request.onreadystatechange = callbackfunction;
  http_request.open('GET', url, true);
  http_request.send(null);
}