by killing enemies, if your talking about online
play search and destroy
In Call of Duty 4: Modern Warfare, the M14 rifle is unlocked at Level 46 in multiplayer.
Just level up, they start at Lvl 4
15+ i think
level 4
Level 38, Lt. Colonel 1
Its where you give up all your guns become a level 1 and get like a new badge.
depends if you are refering to live or what
Kill the boss in the last level.
You have to get to level 4.
Yes, you can level up online just like for the xbox 360, ps3 and computer. I know this for call of duty 4 and 5 for the wii but have never played call of duty 3 or prequals so don't know about them.
Play a lot of Search and Destroy it is by far the easiest way to level up.