At the 'Level Select' screen go down to the bottom option of 'Enter Password' and input following case sensitive passwords (without the quotes) to enable the corresponding effect.

Stage 02:
Enter 'DELIVER'

Stage 03:
Enter 'FIRSTBLUD'

Stage 04:
Enter 'PACKAGE'

Stage 05:
Enter 'OVERLAND'

Stage 06:
Enter 'BOYRACER'

Stage 07:
Enter 'THEHEIST'

Stage 08:
Enter 'BIGCHEESE'

Stage 09:
Enter 'MONKEY'

Stage 10:
Enter 'LEFTFIELD'

Stage 11:
Enter 'INCOMING'

Stage 12:
Enter 'THEFUZZ'

Stage 13:
Enter 'DESERTED'

Stage 14:
Enter 'SNATCH'

Stage 15:
Enter 'GRAB'

Stage 16:
Enter 'ROCKNROLL'

Stage 17:
Enter 'HEREWEGO'

Stage 18:
Enter 'OVERKILL'

Stage 19:
Enter 'DIAMONDS'

Stage 20:
Enter 'RALLYRIOT'

Stage 21:
Enter 'OFFROAD'

Stage 22:
Enter 'SNOWJOKE'

Stage 23:
Enter 'ICYKILL'

Stage 24:
Enter 'LATENITE'

Stage 25:
Enter 'CONTRA'

Stage 26:
Enter 'FBEYE'

Stage 27:
Enter 'DANGER'

Stage 28:
Enter 'ALLOVER'

Stage 29:
Enter ' ATLAST'