At the 'Main' menu go to the 'Level Selection' screen and enter the following codes to unlock the corresponding level.

Unlock Boot Camp:
Enter BOOTCAMP

Unlock Dinner Table:
Enter DINNER

Unlock Bridge:
Enter OVERPASS

Unlock Refrigerator:
Enter COOLER

Unlock Graveyard:
Enter NECROPOLIS

Unlock Castle:
Enter CITADEL

Unlock Tan Base:
Enter MOUSE

Unlock Revenge:
Enter ESCAPE

Unlock Desk:
Enter ESCRITOIRE

Unlock Bed:
Enter COT

Unlock Plasticville:
Enter BLUEBLUES

Unlock Toy Shelf:
Enter BUYME

Unlock Cashier:
Enter EXPRESS

Unlock Toy Train Town:
Enter LITTLEPEOPLE

Unlock Rocket Base:
Enter NUKEM

Unlock Pool Table:
Enter EIGHTBALL

Unlock Pinball Machine:
Enter BLACKKNIGHT