function createXMLHTTP(){
try{
  ajax = new ActiveXObject("Microsoft.XMLHTTP");
  } 
  catch(e){
  try{
  ajax = new ActiveXObject("Msxml2.XMLHTTP");
  alert(ajax);
  }
  catch(ex) 
  {
  try{
  ajax = new XMLHttpRequest();
  }
  catch(exc){
  alert("Esse browser não tem recursos para uso do Ajax");
  ajax = null;
  }
  }
  return ajax;
  }
            
            
  var arrSignatures = ["MSXML2.XMLHTTP.5.0", "MSXML2.XMLHTTP.4.0","MSXML2.XMLHTTP.3.0", "MSXML2.XMLHTTP","Microsoft.XMLHTTP"];
  for (var i=0; i < arrSignatures.length; i++) {
  try {var oRequest = new ActiveXObject(arrSignatures[i]);
  return oRequest;
  } catch (oError) {
  }
  }
  
  throw new Error("MSXML is not installed on your system.");
  }