99 Lives:
During gameplay hit pause and enter the following at the menu:
INVENTORY
Then press square(x6) circle up circle left circle right circle

LEVEL SELECT:
Pause the game, then go to inventory and press:
square, square, circle, square, left, right, left, right, circle, up, right, down
When you go to the baloonist you should be able to select any world.

Run Fast:
During gameplay press and hold:
run and jump

Crash Bandicoot 3 Demo Screen:
Goto the Press Start screen. Then just press L1 and Triangle