Edit the file hitmancontracts.ini with a normal text editor and add two lines:

 EnableCheats 1
 EnableConsole 1

 Save and start the game. Now press [Shift][Esc] to get into the cheats menu. Use the
 arroe keys to activate the codes:

 IOISLO        Slow motion
 IOIER         Bomb
 IOIHITLEIF    Restore life
 IOIHITALI     Box mode
 IOILEPOW      ?
 IOIGRV        Gravity
 IOINGUN       Nail Gun Mode
 IOIPOWER      Mega Force Mode
 IOIRULEZ      God Mode
 IOIPENNY      ?

 ---

 Open the console in the game and type in:

 god 1          God mode
 invisible 1    Invisibility
 giveall        All weapons and items
 give some      Most weapons and all ammmo
 end level      Level skip
 nailgun 1      Enables Nail gun (nailgun 0 disables)
 infammo        Unlimited ammunition
 give x         Spawn the indicated item, where x might be
                weapon_ak47
                weapon_aug
                weapon_awp
                weapon_deagle
                weapon_elite
                weapon_famas
                weapon_fiveseven
                weapon_g3sg1
                weapon_glock18
                weapon_m3
                weapon_m4a1
                weapon_mac10
                weapon_mp5navy
                weapon_p228
                weapon_p90
                weapon_scout
                weapon_sg550
                weapon_sg552
                weapon_tmp
                weapon_ump45
                weapon_usp
                weapon_xm1014