I hope you guys have very very strong computers since modding graphics like that use up more power than usual graphics of their kind since they probably haven't been optimized with GPU's and the game.
Also, you might crash a lot if you heavily mod the game. You also might not.
Just a friendly disclaimer.
There has been a wip mod for the last few years. Last I checked it was still only capable of just getting two people into the world. No quests, NPCs, enemies, or anything. Just the world and two naked people.
And in the end their goal isn't to make a multiplayer mod, but a multilayer "framework" that other people can use to create multiplayer mods. Its more targeted towards tram death match type **** .
Its going to be a very long while before a multiplayer mod is available for Fallout 3.