I'M NOT the creatore of this mod, i just uploaded it here because is hard to find, by the way. i have realized that many morrowind's mod page have been exexpiring, so it's would be a shame if this master piece get lost with the time so easly,  especially due this is probably the only mod that allows the PC to join the Dark Brotherhood in a lore friendly way, as a DB lover...

For not stealing the credit to the original creator, I recommend download it from the original source,
unless it get expired.
 
http://mw.modhistory.com/download-26-12879
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original description
>>>>>This mod allows the PC to join the Dark Brotherhood, to engage in several quests including ten murder contracts and several special
assignments. It is largely dialog-based, and there are journal entries for everything. There are some new (familiar?) faces and some more detailed personalities for relevant characters already in-game. You will join a new group of the Dark Brotherhood family, arrived from Cyrodiil to clean up the Vvardenfell Brotherhood, which seems fixated on Mehrunes Dagon and follows a mortal Imperial woman who calls herself the Night Mother. I tried to bring the feeling of the Oblivion Brotherhood to Morrowind in a lore-compatible, logical, and hopefully fun way.  

This mod has been cleaned with TESAME and the Enchanted Editor.  

This mod will not break any quests from Tribunal or Morrowind. I have done nothing to affect the Dark Brotherhood questline in Tribunal, or the Brotherhood in Mournhold at all. The idea is that the Brotherhoods in Vvardenfell and the mainland (Mournhold) operate independantly (which they seem to do in the vanilla game anyway). Targets of murder contracts are not essential to other quests; the only overlap is with a few targets of Morag Tong special duties. One can still join the Morag Tong and the Dark Brotherhood. The only quest affected is the haunted house one for the Imperial Cult--- but that's not broken at all, because I simply moved Galos Heleran's ghost into Nedhelas' house instead of the basement (I thought his basement would make a good DB hideout). So you can still do that quest if for some reason you are in the Imperial Cult and the Dark Brotherhood.  do not know of any conflicts between any major mods and this one.  

This is my first publicly released mod, and I got a lot of help from the Scripting for Dummies manual and from Srikandi's dialog tutorial, both of which are online. I do not know how to create new meshes, so I used preexisting Bethesda ones for my new weapons/enchanted objects etc.  
 
The three new faces were originally created by Emma, and modified by me. They were used with her permission (thanks!!!) I also recolored two new
hairs from Better Heads hairs (changed to black and red, respectively). This will not overwrite anything or affect any other characters. 

NOTE: I use Westly's DB armor replacer in my game, but it is NOT included and certainly not required. I do recommend it for the most Oblivion-like look, though.
Changelog:v. 1.1 - 1.4 = Fixed textures and meshes.  
v. 1.5 = Dialog/quest reward tweaks.<