Problems With Url Rewriting

Hi,

I am quite new in url rewriting and I have a problem.

I have a "lang" parameter which is used to modify the language in each request. If I write the following the site doesn't display well (images are not shown)

      'urlManager'=>array(
	     'urlFormat'=>'path',
            'showScriptName'=>false,
            'rules'=>array(
                '<lang:\w+>'=>'site/index',
                '<lang:\w+>/<action:\w+>'=> 'site/<action>',
            ),
	),

However if I change the slash of the second rule (/) to a hyphen (-) works well:

      'urlManager'=>array(
	     'urlFormat'=>'path',
            'showScriptName'=>false,
            'rules'=>array(
                '<lang:\w+>'=>'site/index',
                '<lang:\w+>-<action:\w+>'=> 'site/<action>',
            ),
	),

Does anybody know the explanation of this error? I would like the rule with a slash, not a hyphen