Address : http://docs.joomla.org/Adding_JavaScript_and_CSS_to_the_page
$document =& JFactory::getDocument();
$document->addStyleSheet($url);
$document->addScript($url);
ورژن های جدید
// Add a reference to a Javascript file // The default path is 'media/system/js/'
JHTML::script($filename, $path, $mootools);
// Add a reference to a CSS file // The default path is 'media/system/css/'
JHTML::stylesheet($filename, $path);