function createXHR()
{
  var xmlHttp = null;
  // Mozilla, Opera, Safari sowie Internet Explorer 7
  if (typeof XMLHttpRequest != 'undefined')
  {
  xmlHttp = new XMLHttpRequest();
  }
  if (!xmlHttp)
  {
  // Internet Explorer 6 und älter
    try {
        xmlHttp  = new ActiveXObject("Msxml2.XMLHTTP");
        }
    catch(e)
    {
      try
      {
      xmlHttp  = new ActiveXObject("Microsoft.XMLHTTP");
      }
      catch(e)
      {
      xmlHttp  = null;
      alert('Error createXHR()');
      }
    }
  }
return xmlHttp;
}