/**
 * Bridge XMLHTTP to XMLHttpRequest in pre-7.0 Internet Explorers
 */
if( typeof XMLHttpRequest == "undefined" ) XMLHttpRequest = function()
{
  try{ return new ActiveXObject("Msxml2.XMLHTTP.6.0") }catch(e){}
  try{ return new ActiveXObject("Msxml2.XMLHTTP.3.0") }catch(e){}
  try{ return new ActiveXObject("Msxml2.XMLHTTP") }catch(e){}
  try{ return new ActiveXObject("Microsoft.XMLHTTP") }catch(e){}
  throw new Error("This browser does not support XMLHttpRequest or XMLHTTP.")
};
 
// ...

/**
 * AJAX Function
 */

function ajax(url, vars, callbackFunction)
{
  var request =  new XMLHttpRequest();
 
  request.onreadystatechange = function()
  {
    if (request.readyState == 4 && request.status == 200)
    {
      //alert('WORKING');
      if (request.responseText)
      {
         callbackFunction(request.responseText);
      }
    }
  };
  request.open("GET", url, true);
  //request.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
  request.send(vars);
}

// ...