On the main screen select Cheat Codes and then highlight the code you wish to activate. Press circle to bring up input screen and then input the following codes to activate the cheats.
INFINITE LIFE
X, square, triangle, X, circle
SIGHTS
circle x2, X, triangle, square
SNIPE
square, circle, X, triangle, circle
MEGA-SHOTS
circle, triangle x2, square,X
RAPID FIRING
square, triangle, X, triangle, circle
BOUNCES
circle, square, circle, triangle, X
I hope these help!!!