Go to password screen and enter one of the following passwords, 

NAEMMAAB for (ziggurat) 
MAGDIEAH for (backstab)
NINKPDME for (fall n arch)
MJKKAMKC for (fugitive)
JODPIGEH for (rainbow)
ICJPABNA for (lavapalooza)

You will also start the level with enough men to beat each easily. Use the X button to start game after entering password. 

Enter the main menu screen and press the following - SQ, LEFT, SQ, RIGHT, CIRC, DOWN, CIRC, UP.

Now go to GAMES OPTION and select SOLO SURVIVOR on one player mode and your lives will never go down.

go to password screen and type the following for an extra board: jodpegea

(Cody)

MORE SOLO LEVEL PASSWORDS:

Passwords for: 
Ziggurat (begins with board 6) CBIJCLEA 
Backstab (begins with board 11) INJEIEIN 
Plasm Chasm (begins with board 16) NDAJHDID 
Fall N Arch (begins with board 21) BJABGEME 
Fugitive (begins with board 26) BDMIMFAG 
Rainbow (begins with board 31) GHPPLFKB 
Lavapalooza (begins with board 36) ADKPABHI 
All of these passwords take you to that point in the game with a pretty good darn amount of lives and points (Lavapalooza
starts you with 8 lives and 100300 pts!). 
One more tip: When using the infinite lives code, the game will not let you save. But if you want to use the code for practice or
to see the next few sets of boards etc. you can enter the inf. lives code and THEN load a previous game or use a password &
start there instead of at the beginning every time. 

(Bob)

Infinite Lives:
Go to the Main Menu screen and press the following:
S, Left, S, Right, O, Down, O, Up.
Now go into the Games option and choose Sole Survivor. You'll have chosen the one-player mode, but your lives
will never go down.

Desperation moves:
Each character has a desperation move which can be performed when your life meter is flashing. To activate it,
press the R1 and R2 buttons simultaneously. 

Special moves:
There's an easy way to activate special moves too. Simply press R2 plus a directional key. For example, R2 plus
Right, R2 plus Left and R2 plus Down will all activate various special moves.