Unlock parking levels:

Beat each of one of the four parking levels to unlock a 5th parking level. Beat the 5th parking level to unlock a sixth parking level.

Cheat from cheatBook

---

Unlock more parking levels
--------------------------
Finish the four parking levels to unlock a fifth parking
level. If you finsih that as well, you will unlock a sixth
parking level as well.

Unlock the Nippon Maru
----------------------
At the title screen, hold X and press Start. Dont release X
until the mode selection screen appears
-or-
Beat the game with all four characters to unlock the Nippon Maru