cmak is basically the same game as cmbb, just different countries, terrain, equipment.
battle and op files have different file extensions and cannot be interchanged.
because you need the cd in the drive to play either game, you need two drives or exit one game and start the other. theoretically with two drives you could start one game, minimize it, then start the other, but it might take a lot of computer to do that.
that being said, if you want to play the allies other than soviets, get cmak.
worth every dollar imho