How not to resize part of the stage?

Hello, I would like to know how to have a part of my website not resize with the browser window.
You can see what I want to achieve on the website…
They show their work as the page´s background which can be resize with the browser window, but their navigation always stays the same.

I know how to achieve the resizing effect, but it resizes the whole stage including navigation.

Any suggestions?

Thanks, Marcelo.

PS: I´m using flash CS3/A.S.2