* * * Out of sheer curiosity, I would like to know what the various differences are. * * *
This article written by Dick Metcalf and published in the June 2000 edition of Shooting Times may be of interest:
http://hunting.about.com/od/guns/l/aast9mmv380a.htm
And here is a link to another discussion, some of which speaks to specific dimensional differences in the two rounds:
http://answers.yahoo.com/question/index?qid=20080127072915AALxQBt
Edit: Don't get me started on this stuff. ;)
(http://i2.photobucket.com/albums/y30/RichardS/Cartridgespecs9parabellum.jpg)
(http://i2.photobucket.com/albums/y30/RichardS/Cartridgespecs380ACP.jpg)