Layout width

[jackoby]

Hi,
Forgive me if this is apparent, but I can't seem to figure this out.
I want two bands on a web page that span the entire browser width (one on the very top containing logo and navbar, and one on the very bottom) and i want the content on the bands and the main content to be centered with a fixed width.

Thanks in advance,

[drhowarddrfine]

In the css for the elements:
#nav{
width:500px;
margin:0 auto;
}