In the password screen enter these cheats
Semime-semi truck
Snowme-snow truck
Limome-limousine
Quatme-audi quattro
Armyme-army truck
Beetme-a car
Bmrme-bmw
Bnzme-mercedes-benz
Bugme-volkswagen bug
Citme-citrogen
Jepme-commanche pick-up truck
Lcme-landcruiser
Mazme-mazda miata
Vanme-mini van
Vovme-volvo stationwagon
Yjme-jeep
Cratme-wooden crate
Outhme-out house
Tramme-tram
Trexme-trex
Wagome-wagon
Logme-a log
Busme-bus
Stdame-stand a
Stdbme-stand b
Type U instead of ME and the second player can access cars.