PERFECTLY CENTER DIV

<style>

html, body {
    height: 100%;         /* required */
}
body {
    text-align: center;   /* horizontal centering hack for IE */
    padding: 0;           /* required to "hide" distance div */
    margin: 0;            /* required to "hide" distance div */
}
div#distance {
    margin-bottom: -10em; /* half of content height */
    width: 1px;           /* required to "hide" distance div */
    height: 50%;          /* required */
    float: left;          /* required */

}
div#content {
    position: relative;   /* positions content on top of distance */
    text-align: left;     /* horizontal centering hack for IE */
    height: 400px;         /* required - desired height */
    width: 500px;          /* required - desired width */
    margin: 0 auto;       /* required */
    clear: left;          /* required */
}
</style>

<body>
   <div id="distance"></div>
   <div id="content">
Content Here
</div>
</body>