How to make the Header width fluid (100%), but keep everything else fixed (980px)?

I'm trying to make my entire header stretch to 100% fluid width, but keep everything else at a fixed width of 980px.

I've pretty much screwed around with everything and can't seem to make it happen.

I would have thought for sure that putting the following CSS insert would have done it:

#bodyrow {
width: 980px;
margin: 0 auto 0 auto;
}

But it doesn't.

So... how exactly would I make this happen?

Thanks in advance for any help.