// adapted from http://jibbering.com/2002/4/httprequest.html
function getXmlHttp(){
  var xmlhttp;
  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 getUrl(url, cb) {
  var xmlhttp = getXmlHttp();
  xmlhttp.open("GET", url);
  xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == 4) {
      cb(xmlhttp.status, 
         xmlhttp.getAllResponseHeaders(), 
         xmlhttp.responseText);
      }
  }
  xmlhttp.send(null);
}