Put the text "KingPin" on your bike then start a
race, if you do a doughnut long enough you will
make something that looks like a ball of string.
To unlock some mini-games (the ones from Moto GP and a couple others), go into
options menu and watch the text (not video) credits. Scroll down until you get to
the credits for the mini-games. When it appears onscreen, press A. To confirm
correct code entry, the screen with the "Mini Games" title will have the "A"
in "Games" change to resemble that found that controller button.