Anyway, here is a cool article I found in a similar vein (I mean to post it around Halloween, but of course time got away from me!). Scientific Reasons to Believe in Vampires, Zombies, and Werewolves. It's also timely because every time I turn around there seems to be a new vampire TV show or zombie movie.
Personally, I like the vampires = rabies infection theory. That would really disappoint all those Twilight-obsessed teenagers, wouldn't it?
And for those who really prefer zombies, here's another cool one: 5 Scientific Reasons a Zombie Apocalypse Could Actually Happen. It lists 5 parasites/diseases/toxins etc. that could cause a zombie-like state. Somebody really likes zombies to have researched them this much!