My advise would be:
In the CSS, cut the background-image that is now on the div .menu wrapper, and put it on the nav ul (prevent it from collapsing by letting it float):
#access ul {
background: url(images/menu-bg.png) repeat-x;
float: left;
}
Now there is no need anymore for the width declaration on line 38 that overrides the one on 31,
.menu {
/* width: 636px; */
}
for now the background only stretches ‘as far as where the ul list goes’. (Separating aesthetic and structural concerns in this way).
If you don’t mind, I would also advice checking the HTML markup with W3C’s validator, for some of the markup errors will lead to inconsistencies in different browsers, like nesting p in span tags, forgetting to close </div> ‘s etc.
