Javascript: Easy Popup Windows
This easy to follow inline JavaScript is a popular way of letting your users see additional information without navigating away from the current page. With Javascript you can specify the dimensions, visible toolbars, and scrollbars of this newly created window. It can used to show images or HTML documents.
If you are using the Javascript to display images, you will want the width/height dimensions to be about 10 pixels bigger than the side of the image to prvent visable scrollbars.

<p style="text-align: center;"><a href="javascript:void(0)" onclick="window.open('img/tutorials/popwindow.jpg','enlarge','width=510,height=380,menubar=no,status=no,scrollbars=yes')" title="Snuggle Time"><img src="img/tutorials/popwindow_thumbnail.jpg" width="150" height="111" alt="Snuggle Time" style="padding: 3px; border: 1px solid #dddddd;"></a></p>