[As I have never played the game, I am quoting this cheat information
 verbatim.  I edited only for looks.  -Ed.]
 
In the black and white copyright screen, type : AICULEDSSUL
 
You should hear a chime.
Then on the next few screens, you can hit F9 to bring up the cheat screen.
 
SECRET CHARACTERS:
~~~~~~~~~~~~~~~~~~
Both Jade and Smoke can be seen in the Living Forest when they look out
from behind the middle trees.  They occasionally drop down during a
match and give clues on how to reach them.  After you win or lose to any
of the secret characters, you are returned to the Choose Your Fighter
screen where you may pick another character. .