i dont know about Joomla. but for wordpress the best thing to do is to just code it in like i did with this http://jericosystems.com/2008/06/23/gunmetal-wordpress-theme/
Check: http://tools.uvumi.com/dropdown.html
Add: Mootools + The Dropdownscript + The necessary CSS
Assign the script to work with #your-menu. Create your pages as normal and create subpages for the pages that you want dropdowns on etc.
Good luck!