GregF,
Have you set up a webserver (not part of this plugin - there exist other plugins for this)? have you installed phpvirtualbox (also not part of this plugin - no need for plugin just extract to your webserver location)?
once you have you should access your unRAID server address (not 127.0.0.1) and path of your webserver.
See here:
http://vbox.a1aina.com/install.php "Setup a web server" and "Download phpvirtualbox" although the download location has changed to http://sourceforge.net/projects/phpvirtualbox/