This option is not built-in to Publisher. Some people have successfully used
the 'Insert > HTML code fragment' tool to insert dynamic menu code into
Publisher webs. Google for 'javascript menu' or 'DHTML menu' and you will
get a lot of references that you can try.
www.dynamicdrive.com is one good
source of javascript code.
You should research the use of javascript menus before you decide to use
them. There are some obvious advantages, but there are disadvantages and
some argue that you should not use them for a variety of reasons. Sometimes
it is best to just keep your navigation simple and straightforward...
DavidF