Unless I'm mistaken, Lingua::Ispell is a wrapper arround the unix program ispell (Either that, or a re-implimentation)

As far as the difference between a personal dictionary and a regular dictionary, refer to the ispell documentation: man1 man5

It's not immediately obvious from most user level documentation how to make a new dictionary.... you'll have to get the source for ispell and use the buildhash & munchlist scripts. (Or if you want to make an I18N dictionary, take a look at buildict.pl)