O.K. So, yes this is server dependant, but like was mentioned before, the chances of your server NOT supporting SSI are real slim, so try this first.

Make a new page with just the HTML/code for the menu. Now on all the pages that you want to put that menu on add a line like this in the spot the menu would sit...

<!--#include file="included.html" -->

Then save the page with the extension ".shtml". It won't work if you don't change the extension. That should do it.