function createRequestObject()  {
  var req ;
  if(window.XMLHttpRequest)  {
    req = new XMLHttpRequest() ;
  }
  else if(window.ActiveXObject)  {
    req = new ActiveXObject("Microsoft.XMLHTTP") ;
  }
  else  {
    alert('Problem creating the XMLHttpRequest Object!') ;
  }

  return req ;
}

var http = createRequestObject() ;