Are you using wp 3+ nav menus? Meaning, can you go to your dashboard/appearance/menus? If so, just change the order there. If you are not using them, you should. They make life soooooo much easier.
Check out how to register them how to call them in your theme
and how it all looks like when you get to use them.
Hope that helps. If not, just add the code you are using for displaying menus