Near the beginning of the game, after entering the building, you get a signal saying that you should investigate Room 108.
Go to Room 108 and investigate the computer. The computer password is: 5232
Go to Room 018 in the basement after going through the story and finishing Helena's dream sequence. The code for the room is 2689. When you enter the room, get the hard disk from one of the lockers behind the work table. It should be one of the lockers facing you.
Insert the hard disk into the computer and enter disk C and input the Password: 12345.
Input System - Portkey.EXE. The first password is 1944 and the second Password is 0123
Go back to the beginning and open disk V. Enter OPENDOOR.bat. Needless to say, a bunch of weird stuff happens.
Leave the room and the achievement should unlock after 30 - 60 seconds.