<script type="text/Javascript">
var dayslength = 1000*60*60*24; // er, nevermind about that
var start = new Date('9/8/2006').getTime();
var now = new Date().getTime();
var end = new Date('6/20/2007').getTime();
var percent = Math.round((now-start) / (end-start) * 10000) / 100 + '%');
progress = getElementById(progress);
progress.style.width = percent;
</script>
<div style="height: 100px; width: 400px; background: #666;">
<div id="progress" style="height: 100%; float: left; background: #000;"><script type="text/Javascript">document.write(percent)</script></div>
</div>