Infinite Ammo:

While playing any level. press X, Circle, 
X, Circle, Square, Triangle then Start.


Invincibility:

Press pause and hold R1 and don't let go,
then press X, circle, X then it will 
unpause it by it self


Unlock all Levels:

At main menu press L1-R2-L2-R1-circle-
square-triangle-trianlgle then L1+L2+R1+R2
at the same time.  This will unlock all 
levels & give you access to cheat codes.  
(you must complete each level to gain 
cheat codes).