Its not the menu system itself thats at fault.
In php you could use <?php include("menu.php"); ?> (menu.php being what ever the files called) plenty of tuts can be found on google.
HTML server side includes could work, for example <!--#include virtual="insertthisfile.html" -->
Alternatively, if you're using dreamweaver, use the template system.
On a separate note, the pages jiggles when the css menu is invoked, best to play around with padding/margin to make sure theres enough room for the menu to appear in to prevent this.