To use cheats, pause the game (press ESC) and then just enter them:

All Modes:

fogging-Fogging on/off
followme-Move Camera
painless-God Mode

Sharpshooting Mode:

ammo-Unlimited Ammo
autoreload-Autoreload on/off
autofire-Autofire on/off
slowmo-Enemies are Slower
slowrocket-Rockets are Slower
weapons-All Weapons

Driving Mode:

chantastic-Drive Faster
freeze-Toggle Timelimit
ghost-Drive Through Walls
nitro-Unlimited Nitro
snow-Snow
susonly-Drive Only With Tires

Action/Adventure Mode:

ammo-Unlimited Ammo
followterrain-Jump as High as You Want
fragyuck-More Blood
freeze-Freeze Enemies
fps-First Person Perspective
ghost-Walk Through Walls
laser-Toggle Laser Targeting
mrbones-Become a Skeleton
shocked-Become Electric
targeting-Toggle Auto Targeting
weapons-All Weapons
bighead-Big Heads