The following codes must be entered at the Cheat Menu

Invincibility 

Left, Square, Up, Triangle, Right, Circle, Down, X.

Infinite ammunition 

Down, X, Left, Circle, Down, X, Left, Circle.

Invisibility 

Left, Square, Right, Circle, Left, Square, Right, Circle.

Slow-motion mode 

Right, Square, Up, Triangle, Right, Square, Up, Triangle.

Alien mode 

Up, Triangle, Up, Triangle, Up, Triangle, Up, Triangle.

Xen gravity 

Up, Triangle, Down, X, Up, Triangle, Down, X.

12/10/01