Centered Popup Example

<script type="text/javascript">
function CenteredPopup(sUrl,iWidth,iHeight)
{	var x = (screen.availWidth - iWidth) / 2;
	var y = (screen.availHeight - iHeight) / 2;
	var sOptions = "left=" + x + ",screenX=" + x;
	sOptions += ",top=" + y + ",screenY=" + y;
	sOptions += ",width=" + iWidth + ",height=" + iHeight;
    return window.open(sUrl, 'popup', sOptions); 
} 
</script>

<p>
<a href="javascript:var w = CenteredPopup('http://dhtmldev.com',800,335)">Open centered popup
</p>