Emilio,

Welcome to the bbs.

Miller is of course correct. The gun was made by Henri Pieper.

Here is a similar gun.



Here is the Pieper patent application:
http://www.google.com/patents?vid=USPAT246195&id=QiBMAAAAEBAJ&dq=henri+pieper

An english language Pieper Catalog:


A german language Pieper Catalog:


The only reason the Beretta looks similar is method of joining the barrels. Which Pieper changed only in appearance:


So to answer your question. No you did not find the Original Beretta Diana shotgun. Beretta's current offering is merely drawing on a long history of fine European gun making.

By the way, it really is easier if you post images of guns you have questions about. Here is the FAQ:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=6339&page=1#Post6339

Pete