Open the file HITMAN2.INI and enable the console by setting the following two lines:

EnableConsole 1
EnableCheats 1

Then, when in game open the console by pressing tilde key (~) and type in the following cheats:

IOIRULEZ - God Mode (on/off)
IOIGIVES - All Weapons and Items
IOIHITLEIF - Health
IOISLO - Slow motion (on/off
IOIER - Bomb Mode (on/off)
IOIHITALI - Ali Mode (on/off)
IOILEPOW - Special attack Mode (on/off)
IOIGRV - The force of gravity Mode (on/off)
IOINGUN - Nail rifle
IOIPOWER - Mega Power