Frag Zombies is a set of rules for combining Steve Jackson's Frag game with Journeyman Press' Zombies! board game. Of course, ownership of both sets is required, so I'm not sure how useful it will be.
O.K. So it's not miniatures, but anyone my age will remember the classic SPI game "Dawn of the Dead." There's a downloadable version here.
Ok. This is neat. It's a Java window that shows how fast one infected individual can destroy a population.
Zombie Infection Simulation v2.3