There are a lot of skins included with mojoPortal (34 the last time I checked). These skins show many different menu systems, if you look through the skins, you will probably find a menu system close to what you want. mojoPortal v2.3.0.8 and later has a "Preview/Browse" link next to the Skin option in the Site Settings. This nice little feature allows you to scroll through the skins available in your installation without needing to set the skin for the site.
If you decide you like a menu system in a particular skin but you have trouble getting it to work in your skin, let me know what skin you are working with and what problems you are having. I might be able to help you.
The skins included with mojoPortal v2.3.0.8 and later that have "drop down" or suckerfish style menus are:
- jsavard-mojoportal
- jsavard-subblue
- mitchinson-earthy
- mitchinson-earthy-alt1
You can also check out http://www.mojoportal.com/multiple-horizontal-menus.aspx if you want to see how to create a menu like the one used on this site.