Enter the following at the Password

Infinite Lives Screen:
*1NV1S4BL3*

Level 2 Passwords:
Passwords to access this level:
N1PBBDG8V
QQPBBYGYV
Q8QBBYQ6V

Level 3 Passwords:
XG#BVMVFW
GP4BVD6RW
439BBP6LW

Level 4 Passwords:
85DCVLQVC
4GKCVDLZC

Level 5 Passwords:
GNWCVBGMD
6PXCBCVBN

Level 6 Passwords:
SP2CBBVBJ
N93CVBG8J

Start At Boss:
At the Game Options Screen, highlight Start Level. Select the level you want and highlight the Start At Boss option. Select yes and press OK.

Unlock All Levels:
*S3L3CTI0N*

Press OK and immediately go back to the Password Screen and enter the following:
*SH0WT1M#*
and press OK.

Gallery Mode:
#g4ll3ry Unlock all levels: Go to password screen and type as a password #s3l3cton# Press ok, then go back to password screen and type as a password #showt1m3#.

GameShark Codes

Inf Health   
3C29D7C347C2F970  

Inf Lives  
656EBD85D91C838B  

Massive Score   
EA04ACABA798774F  

Must Be On (M)   
7DD7161CFDF9496E
56343CF988CA195A
 

Thanks to Revolution readers timothy and Tommy!