Why does call of duty 4 lag on my macbook when it meets specs?

You're on integrated Intel graphics, which speaks for itself. I don't care what some website says, integrated Intel graphics are too weak to run games, period. They're not intended to run games, and quite incapable. That's why you lag. The fact you're experiencing lag goes without saying. Try on the absolute lowest settings, on a res of 640x480. Intel GMA graphics are good for videos, but not video games. Let me put it to you this way: Trying to "game" on Intel graphics, would be like trying to enter a drag racing contest on a tricycle. You are out of luck, plain and simple.