A mod i'm working on has the Vampire_Berne attached to three NPC's. These NPC's were created by the original author of the mod. I don't know much about vampires and the lore behind them, and I especially don't know anything about the script. Can anyone give me an explanation as to what that script does exactly? And maybe a little information on Clan Berne in general? I'd like to neaten their dialogue up a bit, but i'd like to have an understanding of those things before I go changing or adding anything.

The script adds Spells to the NPC so that they have the Skills/Attributes of a Vampire.
It also checks if Player is the same Clan as the NPC, and changes the behaviour of the NPC accordingly.
It adds +1 kills to your total Vampire kills, which is used for a few Quests. (hence the Journal checks)

http://www.uesp.net/wiki/Morrowind:Berne_Clan at the wiki.
http://www.imperial-library.info/content/vampires at the Imperial Library.

Ahh, ok. When you say changes the behavior, do you mean if the player is a vampire, the NPC will like the player more? I should definitely read up on that a bit more. I don't want to change anything unless I know what's going on, but I also don't want to leave anything in that can't be improved on.

What would be the difference between the Vampire_Berne and Vampire_Berne_PC scripts? I assume these scripts are the same as Vampire_Aundae and Vampire_Quarra, just different clans.

If the player is not of their clan, the NPC will attack. The difference between the scripts is that the pc one adds the spell(s) to the player while the other governs NPC behavior.

Ok, that makes sense. I imagine Morrowind already has dialogue set for vampires of all the clans, so i'll leave that alone. Thanks for the help.