OK well.. I think You can try something like this..
<script language="javascript">
function left_menu()
{
document.write('<a class="menulinks" href=/about.html>Digimon Adventure </a><br>');
document.write('<a class="menulinks" href=/catalog.html>Digimon Adventure 2 </a><br>');
}
function right_menu()
{
document.write('<a href="http://www.onlinedigimon.com" TARGET="blank"><img src="http://www.onlinedigimon.com/images/icon.gif" width="88" height="31" alt="Online Digimon" border="0"></a><br>');
document.write('<a href="http://geocities.com/darklee12" TARGET="blank"><img src="http://www.rikafire.50megs.com/images/TDI2.JPG" width="88" height="31" alt="Digimon Invasion" border="0"></a><br>');
}
</script>
Save it as, for example menu.js
add
<script type="text/javascript" src="menu.js"></script> inside the <head>
tag on each of Your page.
And then replace Your left menu with
<script language="javascript">left_menu()</script> and replace Your right menu with
<script language="javascript">left_menu()</script>
Get the idea?
Now, if You want to change something, just modify menu.js
Gee.. I hope that works, I haven't try it myself though :p