Replicating Bootstraps main nav and subnav

Question

I need to quickly knock up the functionality of the twitter bootstraps main navigation and sub navigation e.g. http://twitter.github.com/bootstrap/scaffolding.html (when you

Answer 1

The two answers above work great, but I just thought I'd let people know that I've made this into a module (without the jQuery dependency) available at ForbesLindesay/booting-sub-nav. It can be used standalone with a script tag or via https://github.com/component/component/