how do I make a function call when the browsers "back" butto

[admin]

I have a web page that uses frames. When you use the native nav bar it is set up to change pictures in other frames when the nav button is clicked. I want certain pictures to always display with certain pages, and my page does this as long as you don't use the browsers "back" button (or "forward" for that matter). How do I force a function call when the browsers "back"/"forward" buttons are hit?

Thanks.