Floating Ad Script ?

hey guys

Do you know how can I make a floating ad that appears in the center of the page and every time the visitor scroll down the page , the ad moves too

 

use a absolutely positioned div;

<div id='ad' style='position:absolute; left : 200px; top : 200px; width : 300px; height : 300px;'>
<!-- ad content here -->
</div>

and some javascript to auto-scroll it

<script type='text/javascript'><!--
window.onscroll = function () { //hope this works, havent tested it
document.getElementById ('ad').style.top = (200 + document.body.scrollTop) + 'px';
}
--></script>