Create a new profile and call it 'Shooterman' ... This'll give you every single level to play in... (PS: i worked it out from the game manual... in the death match screen shots you see the name Shooterman... and so i thought i'd give it a go... and what do you know it worked :) thats what happens when the camel has too much time on his hands... like now really)

Hold L1 on any menu and enter these codes:

Unlocks all movies - Circle, Square, Triangle, Circle, Square
Big Head Enemies - Circle, Square, X, Circle, Circle
One Shot Kill Ability - Circle, Triangle, Circle, Triangle, X

While sprinting, release L3 then immediately switch your weapon. The next gun will automatically appear in your hands.

It should take about four to seven seconds for a grenade to explode. In that time, shoot like crazy. For easier aim (unless they directly in front of you), zoom by pressing R3.

When you die, right before you die, throw a grenade, your timing has to be right. You drop the grenade as you die and it will sit there on your body. Five seconds later, when your killer gets ammo from you, he blows up. A nifty trick to get back at the guy who shot you when they search you for ammo.

Some weapons with a long reload animation can be reloaded faster if the cycle weapon button is pressed right after the reload button. This cuts the animation to the next weapon in the queue, reloading the previous weapon and bringing up the next (hopefully loaded) weapon. By running your weapons in an assembly-line manner, you can reload one weapon while bringing another to bear on the enemy.

In Killzone (multiplayer or single), when you have the shotgun and you are aiming at an enemy, press the primary and secondary fire at the same time. This will fire three shells at one time, capable of killing an enemy from around medium distance. Be warned, however. After doing this twice, you have two shells left, providing less power. This runs your ammo down pretty fast, so try and use it in places like Park Terminal, where you can usually go short distances for more shotgun ammo.

The sniper pistol is the weapon that Luger uses. Because the sniper rifle has a horrible red glow, use the sniper pistol instead. It has less power, but on secondary fire it can take out an enemy with a head-shot.

Beat the 4th mission in the story mode.
Beat the 2nd mission in the story mode.
Beat the 3rd mission in the story mode.