Event.observe(window, 'load', function(){
    var textile_toolbar = new Control.TextArea.ToolBar.Textile('comment_body',{
      preview: 'preview',
          afterPreview: function(){
          Effect.BlindDown('preview');
          textile_toolbar.options.afterPreview = Prototype.emptyFunction;
        }

      });
    textile_toolbar.toolbar.toolbar.id = 'textile_toolbar';
})