Updating a menu across a whole site

Hi, i have created my drop down menu's in Dreamweaver. How can i place this
menu in the top of each page of my site in a way that will allow me to update
one file if changes need to be made to this menu (no frames)? is it done using
style sheets? the site i am building is very simple so i guess i'm after the
easiest solution right now! help appreciated!! Cheers Ray