Online and offline.
Yes.
no , but call of duty modern warfare reflex (cod4) has
Yes
yes
I believe Call of Duty 1, 2 and 3
if you mean offline then no sorry well if it was i would be playing it but i am sorry :(
number one
yes it is for single player offline and multiplayer online if by classic you mean Call of Duty 3 see related link
You can't. But I think you can with Modern Warfare 2's new multiplayer system.
Yes, Call of Duty: Black Ops will have online multiplayer just like many other Call of Duty video games.
No, the leaderboard is for multiplayer online only, anyhting you do offline or in single player doesn't go on the leaderboards.