Diggit Drupalextras

$form['App_create_application']['wrapper-ip'] = array(
    '#prefix' => '<div id="wrapper-ip">',
    '#suffix' => '</div>',
    'ip_application' => application_ip_field($ip,$form),
  );
 
  $form['App_create_application']['addIp'] = array(
    '#type' => 'textfield',
    '#title' => t('New ip'),
    '#description' => t('Liste d\'ip'),
    '#required' => TRUE,
  );

  $form['App_create_application']['addIpSubmit'] = array(
    '#type' => 'submit',
  '#value' => t('Add IP'),
    '#ahah' => array(
      'path' => 'application/js/ip',
      'wrapper' => 'wrapper-ip',
      'method' => 'replace',
      'effect' => 'fade'), 
  );

$items['application/js/ip'] = array (
      'page callback' => 'application_js_ip',
      'type' => MENU_CALLBACK,
      'access arguments' => array('admin'),
      'access' => user_access('admin'),
      'file' => 'includes/admin.inc'
    );

function application_ip_field ($ipList,&$form) {
  if ((is_array($ipList) && count($ipList) > 0)){
    foreach ($ipList as $ip){
      $form['App_create_application']['ips'][$ip]['value'] = array( '#type' => 'item', '#value' => $ip);
      $form['App_create_application']['ips'][$ip]['remove'] = array(
            '#type' => 'submit',
            '#value' => t('Remove'),
            '#ahah' => array(
              'event' => 'click',
              'path' => 'application/js/ip',
              'wrapper' => 'wrapper-ip',
              'method' => 'replace',
              'effect' => 'fade'),
      );
    }
  }
 
  return array(
    '#type' => 'item',
    '#value' => theme('ip_list', $form ), 
  );
}

function application_js_ip ($ip=null) {
  // get the new IP
  $ip=$_POST['addIp'];
 
  // get unique form id
  $form_build_id = $_POST['form_build_id'];
 
  // set false form state
  $form_state = array('submitted' => FALSE);
 
  // get form from cache
  $form = form_get_cache($form_build_id, $form_state);
 
  // create element
  $element=application_ip_field(array($ip),$form);
 
  // add element inside the form (replace)
  $form['wrapper-ip']['ip_application'] = $element;
 
  // save form in cache
  form_set_cache($form_build_id, $form, $form_state);
 
  drupal_process_form($form_build_id, $form, $form_state);
 
  // Rebuild form
  $form = form_builder($_POST['form_id'], $form, $form_state);

  // get new element
  $element = $form['wrapper-ip']['ip_application'];
 
  // get in HTML
  $output = drupal_render($element);
 
  // send HTML to client
  drupal_json(array('status' => TRUE, 'data' => $output));

}