Sadly, it's vaporware. Last time I checked, Interplay (the people that orginally had the fallout franchise) is not looking too well. Infact, I am surprised that they are still kicking around.
There was a talk about a Fallout MMORPG that never got any where.
I did not release that Bethesda rescently got their hands on it.
A few years back, I know that there was promo video released.
Before that, there was FALLOUT TACTICS, however that was release with a lot of unfinished coding. (I do remember downloading the 90Mb Patch that was release 1 week before the game got released)