I have still having some CSS trouble with this and I cannot seem to fix it.
I just made a test page here to see if anyone can help:
The html:
<div class="menu_background">
<div class="menu">This is my menu</div>
</div>
The CSS:
body {
background-color: #FFC;
margin:0;
padding:0
}
.menu_background {
background:url(images/headline.jpg) repeat-x;
}
.menu {
width:60em;
margin:0 2em;
border:solid 1px #F00;
color:#FFF
}
The problem: there is a weird overlapping happening when you shorten the browser window, making it smaller than 60em.
You can look at the test page and here are two screenshots:
1. This is when the browser is full size:

- This is when i shorten the browser window and scroll right:

The best way is to look at my test page and see for yourself.
to avoid that put the background in your menu directly
(review)
to have background 100%