Lurtz is no where mentioned in the books. It is not Tolkien based. I don't know where it came from in the movie - now that I think about it, I'm pretty sure you're right, the name Lurtz isn't in the movie. My guess is he was just given a name so that people could call him something other than "that one orc who was going to shoot Boromir but Aragorn killed him first." Lurtz is a lot easier to say.
It seems like people who make movies do that a lot - for example that one squirrel in Ice Age...