function submitAssignForm(event,form){
  var file = 'data.php';

  var str = getFormValues(form,"validate");
  xmlReq = getXML(file,str, function(xmlReq) {
    if (xmlReq){
      var response = xmlReq.responseXML;
      var response_details = response.getElementsByTagName('response');
      if (response_details.length > 0){
        alert(response_details[0].getAttribute('user_id'));
        alert(response_details[0].getAttribute('purchase_id'));
      }
    }

    return false;
  });
}



function getXML(file,str) {
  var xhr = remoteRequestSetup();
  if (xhr){
    xhr.onreadystatechange  = function(){ 
      if(xhr.readyState  == 4){
        if(xhr.status  == 200) {
          alert('should be working');
          callback(xhr);
        } else alert('Error code ' + xhr.status);
      }
    }; 
  }

  xhr.open( "POST", file, true );
  xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded; charset=UTF-8");
  xhr.send(str);
  return xhr;
}