Here is the sample HTML and Javascript that you guys can use to create a pop up box with dim background using 100% javascript.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Custom LightBox example</title>
<script type="text/javascript">
function showBox()
{
var width = document.documentElement.clientWidth + document.documentElement.scrollLeft;
var layer = document.createElement('div');
layer.style.zIndex = 2;
layer.id = 'layer';
layer.style.position = 'absolute';
layer.style.top = '0px';
layer.style.left = '0px';
layer.style.height = document.documentElement.scrollHeight + 'px';
layer.style.width = width + 'px';
layer.style.backgroundColor = 'black';
layer.style.opacity = '.6';
layer.style.filter += ("progid:DXImageTransform.Microsoft.Alpha(opacity=60)");
document.body.appendChild(layer);
var div = document.createElement('div');
div.style.zIndex = 3;
div.id = 'box';
div.style.position = (navigator.userAgent.indexOf('MSIE 6') > -1) ? 'absolute' : 'fixed';
div.style.top = '200px';
div.style.left = (width / 2) - (400 / 2) + 'px';
div.style.height = '50px';
div.style.width = '400px';
div.style.backgroundColor = 'white';
div.style.border = '2px solid silver';
div.style.padding = '20px';
document.body.appendChild(div);
var p = document.createElement('p');
p.innerHTML = 'Some text';
div.appendChild(p);
var a = document.createElement('a');
a.innerHTML = 'Close window';
a.href = 'javascript:void(0)';
a.onclick = function()
{
document.body.removeChild(document.getElementById('layer'));
document.body.removeChild(document.getElementById('box'));
};
div.appendChild(a);
}
</script>
</head>
<body style="height:2000px">
<a href="javascript:void(showBox())">Toggle box</a>
</body>
</html>