theres cheats for coop as well as single player i beleive, there are these hidden cards scattered around all the levels and each one does something... and once you get them for mutiplayer you can use them for multiplayer coop to... course you can just google or youtube on how to find them all.
and fyi cod4 is better
ftmw
its double xp week for cod4 as well as half price for the mappack in case anyones interested!