Plugin in category layout

Dear Flexicontent staff,
how can you see in this page hiperformancecms.eniac.it/index.php/it/formatori.html i'm trying to "load" a plugin inside a category-view layout (over the green line). This plugin is the standard Phocagallery Slideshow, you can see it "in action" here hiperformancecms.eniac.it/index.php/it/f...y-robbins-prova.html .
I have created a new parameter where the user can insert the plugin (instead that in the category description), a textarea.
Two questions:
- why every text i insert in the parameter is converted in "Array" when i save?
- once i was able to display my plugin text in the right place, how can i force Joomla to "load" the plugin instead of simply write it on screen?
Thanks a lot!