Chances are it is something in your css, but really if I have to figure out how to open your page I'm not going to. Just link it. It's a web page right? Just paste in the link.

mydomain.com wrote:

"My will is far simpler "what, you really have bu**er all money?" ... "yeah, but I've been to the shop and got some sugar ... hold this will you *passes coat* .... so, what were we going upstairs for?"

ooops, wrong paste, hang on :

mydomain.com/try2.ext wrote:

  <div id="credits">
	    <h2>Credits</h2>
	    <p>This README file was inspired by EdB, 
If you wish to show total appreciation for his genius then stop using mydomain.com on the forums,
it gets fucking annoying really fast
and is about as helpful as an ashtray on a bloody motorbike huh?</p>
	  </div>

¥

Ok boyz, go on:

http://radio75.fr/b2evolution/blogs/blog1.php
Here menu is narrowed

http://radio75.fr/b2evolution/blogs/blog1.php/2009/05/04/lundi-4-mai-2009
Here menu is ok

One reason it might be narrowed is because the CSS is told to narrow it...

div.top_menu ul {
/*    float:left; */
    margin: 0 0 0 0;
    padding: 0 0 0 0;
    list-style-type:none;
    font-size: 10pt;
    font-variant:small-caps;
    font-family: Arial;
    font-weight:normal;
    background:#A11C1C;
    line-height:24px;
}

div.top_menu_narrow ul {
    width: 620px;
}

John nails it! Remove that "width: 620" bit and the red goes full width.

Thanks John, you've pointed it!