hello,
I'm trying to center a UL menu using "margin: 0 auto;" but it doesn't work, it's floated to left !
here's the CSS code :

#main_menu {
	background:url(../images/main_menu_bg.jpg);
	height:32px;
	float:none;
	width:100%;
}
/****************************/
/*		Main Menu CSS		*/
/****************************/
#main_menu ul {	
	width: 100%;
	margin: 0 auto;
	padding-bottom: 20px;
	text-align:center;
}

#main_menu ul li {
	display:inline;	
	margin: 10 0 0 0;
	padding: 0;
	list-style: none;
	float: left;
	font-size: 13px;
	background: url(../images/main_menu_bullet.png) no-repeat;
	background-position:left bottom;
}

#main_menu ul li a {
	display: block;
	margin: 0 1px 0 0;
	padding: 6px 10px;
	width: 100px;
	color: #b3b3b3;
	text-align: center;
	text-decoration: none;
}

and here's the HTML :

<div id="main_menu">
        <ul>
            	<li><a href="#1">About MPU</a></li>
                <li><a href="#2">Admissions</a></li>
                <li><a href="#3">Academics</a></li>
        </ul>
</div>

How do you expect to center something that's 100% width ??? You're telling it that the UL will take up the entire available horizontal width, so the margin: 0 auto; is rather pointless.

Get rid of the display:block on the li a and they will line up.
You also need to make sure you CLEAR your float.

Thanks a lot, I specified the width of the UL element now, and it works fine !