What about submenus? Can a button in a pull-down menu then bring about another pull-down menu?
Yes. You often see this in programs nowadays. You can simply place another pull-down movie clip inside your main pull-down movie clip. The new buttons will probably need to be shifted over to the right to avoid covering the buttons of the main pull-down menu. You can go many levels deep this way.
Can you have the pull-down menus slide in?
Yes. Instead of having just two frames , you can use gotoAndPlay and have a series of movements along several frames and a stop() command at the end. You might want to use a mask layer to hide the buttons as they slide under the title. Or, you could have them dissolve in slowly.
Do pull-down menus always have to pull down?
No. The buttons on a pull-down menu can actually expand up, to the side, or in any direction. But some scripts require that the buttons all touch so that the user can move the cursor from one to the other without ever leaving the movie clip.