I think I've been told that Flash for menu buttons is difficult or impossible for disabled people; I can't remember why, perhaps the screen readers for blind people don't work or people without a mouse can't hover over them. I think it's best to use Flash just for visual effect and not for the operation of a page.
I use CSS drop down menus from CSSplay, but I always make sure that the top level has a link somewhere in case the drop down menu doesn't show and then make sure that the page from the top level link has the other links on its page somewhere.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.