What you are describing are dhtml and javascript menus. These are not
supported directly by Publisher, but can sometimes be incorporated using the
insert html code fragment box. You can either google for dhtml menus, or
perhaps start here to read about them:
http://www.dynamicdrive.com/dynamicindex1/

Alternatively, if you just want the text of a hyperlink to change colors on
mouseover, you can just insert the following code snippet via the insert
html code fragement tool:

<style>
a:hover {color: #ffffff; font-weight: bold;}
</style>

#ffffff is the HTML Hex value and can be changed to a color of your choice,
as well as the font weight.

DavidF