There is another thread, but it doesn't have a lot of specific info. showthread.php?t=8690&highlight=wordpress
I did a quick search and it looks like there should be plugins available for wordpress that allow you to execute PHP code in your page. I found this one for example execute-php-in-wordpress-post-page-and-widget-sidebar/. Not sure if that works, but in general I would look for a similar plugin and that should allow you to run the PowerGallery PHP code.