When you enter the first level go into the top left corner by the trash-can and press up you will enter a secret room. Kill all the guys but don't walk any where and one extra life will appear after that wait for about 30-60 seconds and four more will appear.
For a greater challenge, enter the password "MRRYPN".
Hidden Room: Level One
At the beginning of level one, go up to the trash can on the left side of the screen, then push up and jump.
Hidden Rooms: Level Two
When you're on the bridge, before you go anywhere go to the top left-hand corner and do a jump kick. It will bring you below the bridge and let you fight some people and get some goodies.
Another secret room is in the mall. When you get to the statue
punch around the hand or the head. The room should give you 1
extra life, and all of the different helpers.
To start on any level, enter the password "SCBCRS". Note that you can't finish the game this way, as you'll return to the Level Select screen when you die.