mojoPortal comes with a lot of skins with different menu styles. One of these skins (andreasviklund-02) has two sets of horizontal menus allowing for a more compact menu system on 2nd tier pages. You can check out the above mentioned skin using the demo site for a working example. The mojoPortal site itself uses a similar menu system so you can use it as an example also.
I am currently working on my church's website (http://acckc.org/mojo) and it uses this menu style.
To achieve this style of menu, you must add a few controls to your layout.master file.
Place this code under the read more