Those are the Codes used in the PS - Version of the Game or the ArrangeMode on PC (which is just a Port of the PS Version)

1. Lock Numbers

    0426 - Custody Room (The one with a dead guard and also the first save point.
                   Don't forget to hit the switch on the wall first.)
   
    8159 - Louge weaphon storage locker (The thrashed bar in the 2nd floor of the
                   facility)
   
    705037 - The room adjacent to the Louge (You need to  use a DDK here. Once
                     you're inside you'll meet a researcher and use the 2 panel keys on the
                     plaque behind the desk. The letters on panel keys, LEO & SOL, is
                     actually the lock code. Try writing it on a piece of paper or on a
                     calculator then read it upside down.)
   
    7248 - Computer room (Opens the gas chamber room.)
   
    1218 - Stabilizer design room (Use this code on the panel the get the upgrade
                   parts for the shotgun.)
   
    367204 - Forgot which room to use this one. (It is the room where you'll get the
                     parts for the stabilizer and initializer.)
   
    0367 & 0204 - Stabilizer & Initializer  Assembly Room (Use the first code in the
                          computer terminal & the 2nd one in the thing that looks like a
                          large vending machine in the corner.)
   

   2) DDK Codes

    HEAD
    NEWCOMER
    LABORATORY
    ENERGY
    WATERWAY
    STABILIZER
    DOCTORKIRK
   

   3) Registration Numbers

    Paul Baker - 58104
    Mark Doyle - 57036
    Dr. Kirk   - 31415
    
   

   4) Gas Combinations

    RED -defeats-> GREEN
    BLUE -defeats-> ORANGE
    GREEN -defeats-> PURPLE
   
    (Use this in the gas chamber room. Sometimes you have to mix the gases to come up
            with the right colors.)