If you're using an emulator, the instructions will vary
depending on which emulator you're using. Basically,
what you want to do is activate the codes as soon as you
see the "SEGA" screen. If you turn on the codes before
the game starts to load, or if you reset the game with
the codes on, you will get a red screen and the game 
won't run. If you get a red screen, turn the codes OFF
and reset the emulator, then wait until you see the SEGA
screen and turn the codes ON.


The following codes have only been tested on a 1 player
game.

EZ1A-CAG8
Start a new game with 25 credits (instead of only 10).
LB1A-CAG8
Start a new game with 50 credits (instead of only 10).
AJLT-AA7C
Infinite credits!
CB1T-CABC
Start a new game with more life (only works on the first
credit).
LB1T-CABC
Start a new game with much more life (only works on the
first credit).
XF1T-CABC
Start a new game with MEGA life (only works on the
first credit). With this code on, you'll have to be
shot 99 times before you die! (normally, you die after
only 5 shots).