The skin on this site is a modified version of styleshout-brightsideoflife (which is included with mojoPortal), so best to look at that one. The main difference is I made the one on this site wider and I also added a second tier horizontal menu. You can find a similar menu structure in andreasviklund-02, which has 2 levels of horizontal menu then a vertical menu for pages deeper than 2 levels. Look at the css, but also look at the layout.master and the way the menus are setup there.
Hope it helps,