It does come for both systems as well as PC I believe, BUT you can't play on PS3 against someone on Xbox360, not sure if that's what you were asking since you mentioned something about them playing against each other.
PS3 users can only play against other PS3 users, or have a 2nd controller plugged in, same goes for Xbox360.
I really enjoyed the game, now i'm busy playing online (not right this second NOW) but I thought the campaign was WAY to short...
and as much as I love these games, it would be nice if for once you didn't play as either a brit, a ruskie or a yank...just sayin, lots of other countries have rich histories to use for games, and military/covert ops teams to use for games as well.