[jQuery] help for plugin

Hi all, i'm trying to improve my plugin

http://www.pirolab.it/pirobox/

My problem is to create the next and prev buttons function to call
next and prev image, i'm not a programmer and your help would be
great, more brains works better than one :)

here is the script

http://www.pirolab.it/pirobox/js/pirobox.js

TNX in advance

Diego Valobra