Modern Warfare 2 won’t have campaign co-op gameplay but it will have its own dedicated cooperative mode.
The name is Spec Ops, and the game is frenzied, difficult, and fully-engaging. Strategy and skill will determine your level of success in this do-or-die mode. Breaching, fragging, and flanking; you’ll have to master the art of warfare to survive, and that’s the way Infinity Ward wants it.
Check out this developer introduction and explanation of Spec Ops courtesy of GameTrailers.