// JavaScript Document
function GetXmlHttpObject()
{ 
  var objXMLHttp=null
  
  try {
    objXMLHttp = new ActiveXObject("Msxml2.XMLHTTP"); //later IE
  } catch (e) {
  try {
    objXMLHttp = new ActiveXObject("Microsoft.XMLHTTP"); //earlier IE
  } catch (e) {
  objXMLHttp = null;
  }
  }
  
  if (objXMLHttp==null)
  {
    objXMLHttp=new XMLHttpRequest(); //IE7, Firefox, Safari
  }
  
  if(!objXMLHttp)  alert ("Su browser no soporta AJAX."); 
  
  return objXMLHttp;
}