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Actually, ignore the other links, they're usualy can only load on IE, have massive amounts of code, which take ages to load your website.
Try, Smartmenus, it's easy to install, it's browser wide compatible, and easy to set up, and can do virtually anything you want.
I think the link is,
http://www.smartmenus.org ? But try google.
It's free for non commerical websites only, otherwise, you pay $35 for a licence. They guy diserves the money.