First, go into your Playstation or Playstation 2 game browser screen. Insert the game disc and you can listen to some of the audio tracks from the game. Tracks 2 through 34 will play music.
Hold L1, R2, Circle and Start for around five seconds at the main title screen. Then, choose Single Player Mode and select any character. You should be able to play as the game boss.
During Level 2: Move to the left side as far as you can, then hold down & left, R1 and L1 all at the same time and press Start. The screen should blank out, then skip to the last level Boss.