Go to Options/Cheat Codes and enter one of the following codes:
howhardcanitbe0: Difficulty adjust (0 = easiest)
howhardcanitbe1
howhardcanitbe2
howhardcanitbe3
howhardcanitbe4
howhardcanitbe5
howhardcanitbe6
howhardcanitbe7
howhardcanitbe8
howhardcanitbe9 (9 = most difficult)
starpower: Gun (key F by default) and no damage
leatherandlace: Gun, rocket launcher (keys F and H) and no damage
upupdowndown: Unlock all cities, vehicles and modes (arcade only)
theparrot: Unlock all modes
griswold: Unlock all cities
octane: Nitrous
yerbamate: Unlimited Nitrous
rimbuk: Unlock all cities, vehicles and modes (arcade only)
starlite: "hallucinating view"
tumbler: ?
aquaspark: ?
happyhour: ?
operationdoom: ?
quickFix: ?
howfastcanitbe0: Speed adjust ?
howfastcanitbe1
howfastcanitbe2
howfastcanitbe3
howfastcanitbe4
howfastcanitbe5
howfastcanitbe6
howfastcanitbe7
howfastcanitbe8
howfastcanitbe9