Note: You don't need Code Breaker or GameShark to activate them but you need the PS2 version.
To get to cheat mode, hold L2 and R2 together then toggle up and down to choose the number for the code.
All monsters and levels: 141421
One hit building destruction: 071767
All power upgrades: 011235
Demo with two monsters: 082864
Watch intro: 667300
Watch ending: 667301
Disable codes: 000000