Vampire weakness: Recoils from a strongly-presented holy symbol. That's about as vulnerable as a vamp gets to holy stuff, because they're normally high HD with extra turn resistance. It beats me why they haven't taken over settings with divine casters.
Anyway, what's to say the undead want to take over? A vamp is a predator; he hunts humans, and the only time he wants to rule humans is (a) if he's setting up a farm, or (b) if he were a megalomaniac in life; he certainly doesn't want to vamp everyone he sees, because then he can't eat (the ecology is skewed). A lich isn't concerned with temporal power; she's made a decision to pursue magical goals, and (except for the odd army of undead horrors) she will only bother mortals when they have something she wants.
Or maybe she'll rule the world as an eternal lich-empress, but that's unprecedented.
*cough*Gith*cough*
And what's to say the undead haven't taken over already? That would be fun for a homebrew... (I'm not doing it because the undead are important in a slightly different way in my campaign.)