Welcome to the mojoPortal community! We are happy to have you here. You were on the right track. This is a feature of the skin. You will want to take a look at the mitchinson-earthy skin. It really is the best implementation of drop-down menus we have in the included skins. It uses jquery-superfish which works very well in all of the major browsers. Even IE6!
If you want to use the menu from the mitchinson-earthy skin but another skin for your site, just drop a post in the Help With Skins forum and someone will help you out with it.
Hope This Helps,