You don't unlock it you just buy it when you have enough COD points.
In Black Ops multiplayer you unlock the AK-47 at level 38.
It only works if your unlock it, buy it, and use it on player matches
You unlock gold camo in black ops, when you reach prestige level 14, level 25.
You get to level 50
When you rank up to level 35 you will unlock it.
You have to get to level 44 and then pay the $2000 to unlock it
you unlock more emblems
Level 44
get to the level where you unlock it :):P
the crossbow i believe
use the perk 'warlord' or 'warlord pro' to get multiple attachments.
Level 27, for 2000 cod points