Hi,
Just don´t bother about the plugins.dll. It has already been bundled within PhotoPerfect.
In order to implement Photoshop compatible plugins, please just copy all files of that plugin into the main folder of PhotoPerfect. After restarting PhotoPerfect, you will see that the plugin is now shown in the processing resources on the right tool bar (alternatively you can also press F9). Just double-click on that plugin to start. It´s quite easy :-)
Below please find the links to some free plugins:
Virtual photographer
Harry´s filter
On this website you can also find quite a lot of plugins , too:
http://www.thepluginsite.com/
Best regards and have fun trying out
Hoang-Tran