var req;

function loadXMLDoc(url, callback)
{
  // native XMLHttpRequest object
  if (window.XMLHttpRequest)
  {
    req = new XMLHttpRequest();
    req.onreadystatechange = callback;
    req.open("GET", url, true);
    req.send(null);
  }
  else if (window.ActiveXObject)
  {
    req = new ActiveXObject("Microsoft.XMLHTTP");
    if (req)
    {
      req.onreadystatechange = callback;
      req.open("GET", url, true);
      req.send();
    }
  }
}  // loadXMLdoc()