No. The multiplayer is available straight away for you to play. The only things you can gain by finished the Black Ops campaign is the zombie map Five (which can also be unlocked by a cheat).
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In Call of Duty: Black Ops, to go on multiplayer you have to go to multiplayer on the menu that says: CAMPAIGN MULTIPLAYER ZOMBIES OPTIONS
No, But there is a spec ops type thing which is like campaign but is muliplayer.
There is no campaign for multiplayer. There is multiplayer which has no storyline, there is special ops where you can do co-op to do either a kind of campaign with a storyline with a friend or do survival mode to survive as many times as possible, or there is campaign mode, which is a single-player storyline.
Simply go to the black ops multiplayer settings and disable the aim assist
In Black Ops multiplayer you unlock the AK-47 at level 38.