ho fatto cosi ma non succede niente dove sbaglio grazie del tuo aiuto...
<div style="width: 960px; margin: 0 auto;">
<div style="display: block; text-align: center;">
<div id="banner_left" style="display: block; width: 300px; height: 275px; position: absolute; margin-left: 350px; margin-top: 50px; z-index: 2;">
<p id="chiudi" style="cursor: pointer;"><span style="color: #ff0000;"></span></p>

<div id="banner"><script type="text/javascript">// <![CDATA[
document.write('<s'+'cript type="text/javascript" src="http://ad.altervista.org/js.ad/size=300X250/r='+new Date().getTime()+'"><\/s'+'cript>');
// ]]></script></div>
<script type="text/javascript">// <![CDATA[
document.getElementById('chiudi').onclick = function() { document.getElementById('chiudi').style.display = 'none'; document.getElementById('banner').style.display = 'none'; }
// ]]></script><script BANNER </script></div>
<script type="text/javascript">// <![CDATA[
document.getElementById('chiudi').onclick = closeBanner();
setTimeout(closeBanner(),5000);// chiusura dopo 5 secondi
function closeBanner() {
document.getElementById('chiudi').style.display = 'none';
document.getElementById('banner').style.display = 'none';
}
// ]]></script>




</div>
<h2><iframe name="aaa" src="Link Video" frameborder="0" width="607" height="407"></iframe>