function getHTTPObject()
{
  var xmlhttp;

  if(window.XMLHttpRequest)
  {
    xmlhttp = new XMLHttpRequest();
  }
  else if (window.ActiveXObject)
  {
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

    if (!xmlhttp)
    {
      xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
  }

  return xmlhttp;
}

var ajax = getHTTPObject();