how do you align the somthing center

as this can seem to only align lelf or right

/* ********** [ NAVIGATION ] ********** */

div#headernav_wrap {
    height: 60px;
    position: relative; }

    div#headernav {
         }

        div#headernav ul {
            margin: 0px auto;
            padding: 0px;
            width: 650px;
            height: 30px;
            list-style-type: none; }

            div#headernav ul li {
                margin: 0px;
                padding: 0px;
                float: left; }

wanna make it center

thanks