Just add html code in layout column in your blog anywhere and change name of website from www.vxpapps.com to site you wish to add as a popup.
<script type="text/javascript">
| document.body.onclick= function(){ |
| window.open('http://www.vxpapps.com', 'poppage', 'toolbars=0, scrollbars=1, location=0, statusbars=0, menubars=0, resizable=1, width=950, height=650, left = 300, top = 50'); |
| }</script> |