GB_myShow = function(caption, url, /* optional */ width, height, callback_fn) {
  
   defaultURL=url;
	var options = {
        caption: caption,
		center_win: true,
        width: width || 630,
        height: height || 520,
        fullscreen: false,
        show_loading: false,
        callback_fn: callback_fn
    }
    var win = new GB_Window(options);
	return win.show(url);
}