var xmlHttp = createXmlHttpRequestObject();

function createXmlHttpRequestObject() 
{
  var xmlHttp;
  try
  {
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)
  {
    var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
      "MSXML2.XMLHTTP.5.0",
      "MSXML2.XMLHTTP.4.0",
      "MSXML2.XMLHTTP.3.0",
      "MSXML2.XMLHTTP",
      "Microsoft.XMLHTTP");
    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++) 
    {
      try 
      { 
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      } 
      catch (e) {}
    }
  }
  if (!xmlHttp)
    alert("Błąd podczas tworzenia obiektu XMLHttpRequest.");
  else 
    return xmlHttp;
}