Congrats on a great purchase Lor Dric. Best survival horror game to come out in ages.... since Alone in the Dark and Ive played a few; The Legacy, Alone in the Dark 1,2,3, New Nightmare PC, Resi Evils & Silent Hill on the PSX. Takes the enivornmental manipulation of HL2 and puts a fantastically dark story around it, to make it a great experience.
Unfortuantely it only looks like you can register Penumbra Black Plague on the forum. Not sure if your key will work in that slot. If you have seperate codes for eachgame, just try the Black Plague code.
As for order play....
1. Overture
2. Black Plague
3. Requiem
The story demands they be played in order and that you complete the games. Otherwise youll miss out on a bit of a fantastic story.
Dont forget to post back or visit the Frictional (developers) forum for hints.
Enjoy.