I have used joomla pack before to move a site to ispconfig and it worked without problem. I've also tried on other occasions and it's not worked... I know it's not the answer you're after but it's not too difficult to move the sites manually. FTP or tar and move the content, export the database using phpmyadmin. Then create the database and user on the new server with the same details. Just be sure to change the configuration file for the new paths...
