var xmlHttp;

function initAjax() 
{
  try 
  {
    xmlHttp = new XMLHttpRequest(); // Firefox, Opera 8.0+, Safari
  }
  catch (e) 
  {
    try 
    {
      xmlHttp = new ActiveXObject("Msxml2.XMLHTTP"); // Internet Explorer
    }
    catch (e) 
    {
      try 
      {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
      }
      catch (e) 
      {
        alert("Your browser does not support AJAX!");
        return false;
      }
    }
  }
}