Cheat List
Open your Hitman2.ini in the Hitman2 directory in a text editor and add "EnableCheats1" without quotations right below EnableConsole.
You can activate the following cheats by typing them in the game while playing.

IOIRULEZ or IOIRULEY - 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 Mode on/off
IOIPOWER - Mega Power
NOTE: If you have a U.S. keyboard, just type IOIRULEZ. On European keyboards the Z and Y change place so you have to type IOIRULEY.

NOTE: Make sure you don't enter the cheats too fast. Type them more or less slow.

Unlock All missions
Open up Hitma2.ini and change the following line

DefaultScene=AllLevels/logos.gms

into

DefaultScene=AllLevels/levelmenu.gms

Start the game and you will get a level select menu, with all the Missions unlocked.


DEMO CHEAT CODES
Open up your hitman.ini file located in your Hitman directory. Add the line 'enableconsole 1' to the file. When playing a mission, hit the '~' key. Types any of these codes:

god 1 - God mode
giveall - All weapons with max ammo
invisible 1 - Invisibility (0 - off)
infammo - Infinite ammo
commands - List all commands
ip_debug 1 - Debug mode
ip_timemultiplier # - Time multiplier (1 - normal)