"Vampires, zombies... same thing"

I overheard a coworker talking about "I Am Legend" with another coworker, and he said something about the world being overrun by zombies. I said "They're vampires. The (Richard Matheson) story it's based on has it as vampires." and he says "Vampires, zombies, whatever. Same thing." No, they're not. I haven't seen the movie -- maybe they did make them more like zombies? Not sure. But zombies aren't vampires, vampires aren't zombies -- all undead are not created equal!