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i don't agree with d-loc much, but i believe that is the smartest thing i've ever heard him say. Try to play it with two controlers kid, unless you feel the need for your friend to be with you while you wait in suspense.
If they have their own gamertags then yes they definitely can. If not they can probably sign on as a guest and play unranked games or something. (I don't have Call of Duty 2 but thats how all my other xbox games are.)