Before you start the game, you can enter a name for your character. The default name is "PLAYER 0", select it and push enter to rename.  Change it to "GOURANGA", you should hear a chime and then change the name to any of the cheats that you want to enable. You can change it back to the name you want and start the game.

GOREFEST - Enable blood splats
MADEMAN - Max respect for all gangs at start
EATSOUP - Free Shopping (For Car Upgrades etc.)
CUTIE1 - Gives the player 99 lives
ARSESTAR - Keep weapons after death
DANISGOD - Gives the player points for saving,resprays, etc
IAMDAVEJ - Gives the player 9999999 points
MUCHCASH - Gives the player $500,000
SEGARULZ - Gives the player a multiplier of 10
COCKTART - Skip exploding scores
GODOFGTA - All weapons + max ammo
DAVEMOON - Basic set of weapons + max ammo
VOLTFEST - Electro Gun with infinite ammo
FLAMEON - Flame Thrower with infinite ammo
SCHURULZ - Infinite 'double damage' powerup
RSJABBER - Infinite 'invulnerability' powerup
HUNSRUS - Infinite 'invisibility' powerup
JAILBAIT - Infinite 'get out of jail free' cards
BUCKFAST - All dummy chars are muggers
NEKKID - All dummy chars are naked
LASVEGAS - All dummy chars are Elvis!
FISHFLAP - All cars are 'mini cars'
GINGERR - Access to levels one & two
UKGAMER - Access to all three levels
TUMYFROG - Access to all levels + all bonus levels