Type those cheats during the game:

 SW_IWANNABEAJEDIKNIGHT          - God Mode ON/OFF
 SW_PRINCESSLEIAISAHOTCOOKIE     - All weapons accessable
 SW_YODAWANTSTOBEAREALBOY        - All racers appear tiny and green
 SW_EWOKSTURNMEON                - All levels accessable
 SW_THEFORCESUCKS_TRYSCIENTOLOGY - Instant death
 SW_DONTSEEAUSTINPOWERS          - Win current level
 SW_IWISHMYDADDYWASDARTHVADER    - Bonus level (DarkInsemination)
 SW_ICANTBELIEVEIACTUALLYFELLFORTHISCRAP - Message "April Fool's"

 Press at Wattos' shop [Ctrl][F4][4] and you will get 1.000 credits.
 You can repeat this five times max.