Question about long width images

I've got a very long width image,

my html is set out like this,

<div id="wrapper>

<div id="header">

<div id="nav">

<div id="content">


now the header div and content div wont expand to take up the width of the image

how can I do this? hope i've explained it well

thanks

 

I would rather give the image 100% size width to stretch accordingly