Various cheats

Unlock All Levels:
     At the main menu press X, Y, B, Left, Up, Right, L, R

Unlock Weapons:
     Unlock  each  weapon  by completing the corresponding mission and
achieving the Silent Assassin rating.

Weapon        Level
Mission 1     CZ 2000 Dual Pistols
Mission 2     Micro Uzi Dual Submachine Guns
Mission 3     Silverballer Silenced Dual Pistols
Mission 4     Magnum 500 Dual Pistols
Mission 5     Sawed-Off Shotgun Dual
Mission 6     M4 Carbine Silenced Assault Rifle
Mission 7     SG220 .S Dual Pistols
Mission 8     MP5 Silenced Submachine Gun
Mission 9     AK 74 Silenced Assault Rifle
Mission 10    GK 17 Dual Pistols
Mission 11    Micro Uzi Silenced Dual Submachine Guns
Mission 12    PGM Silenced Sniper Rifle

Hints

Live Again:
     When your health bar reaches zero the game will enter a black and
white  death  sequence.  If you are get four consecutive head shots on
four  different  enemies during this sequence you will receive a small
amount of health and return to the game.

Unlock the Mini Gun:
     The  mini gun is held by a patient who is behind the locked doors
of  a  basement  room in Mission 1: Asylum Aftermath. The keycard that
unlocks  the  doors  can  be  found  during  Mission  9:  The Wang Fou
Incident.  It  is called Orthmeyer's Keycard and is on Lee Hong's desk
in  his  office  on the second floor of his mansion. After finding the
card, finish the mission and save your progress. Quit to the main menu
and  replay the first mission. Head to the northern section of the map
and  turn  right in the small room with the red flashing sensor on the
ceiling.  Pass  through  the  west  door and dispose of the patient in
order to collect the mini gun.