<a href="http://www.turnstyle.org/FreeCulture/" target=_blank onClick="MBw=window.open('http://www.turnstyle.org/FreeCulture/','FC_popup','toolbar=yes,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,width=340,height=340'); MBw.focus(); return false">"Free Culture" popup audiobook</a>

Or just add a link to:
http://www.turnstyle.org/FreeCulture/

To download the button, right-click and save-as: