In my rework of the Edge of Night, I've taken a few liberties. One of the things I'm working on at the moment is the reason the Skaven are so interested in Ubersreik.
One consideration was to utilize the "Chest" rumor, and instead of it being a treasure, it was a large chunk of Warpstone buried in a lead chest under the River Tower. The only issue I have with this is that I can't come up with a good reason for the Dwarfs to put it there rather than in a Dwarf Hold.
So then I had the thought that inside the chest could be the head of a Vampire, that for some reason couldn't be fully destroyed and so the head was taken and buried seperately from the body. This would explain the undead in Morr's Garden, perhaps.
So I started turning this over and over and had the realization that I have no idea what happens to the undead when exposed to Warpstone.
Basically I've got a bunch of half baked ideas, and I'm trying to tie them together with a rope that's two feet too short. I know I want to have the Undead in the Garden be real (In fact, an entire section of the Garden is walled off to contain the out-of-control undead population... see the Thief: TDP Down in the Bonehoard (Horn of Quintus) mission to fully understand the scope of my plagarism), and I want the Skaven to have a real reason for coming after the town other than Rasknitt is just bored.
Edit-- The only thing I know about Warpstone regarding the Undead is that Nagash used it (Thus his ridiculous size) and that it was instrumental in the creation of the first vampires. Any other thoughts? Brainstorming session.... begin!