To use a code, type it on a line byi tself in the CSTORM.INI file in the CyberStorm directory. When you load the game a new menu item will appear depending on which code you used.
It's Good To Be The King - Get Mega Credits
Heal Me - Repair all HERCs and pilots
BrownNoser - Skip to the next rank
Herc Me Some More - You can buy all HERCs