The listing, Dead Space PC (Origin, CAN BE ADDED TO STEAM) has ended.
I will send you Dead Space Origin key on listia email as soon as I get online.
This is a Origin key however it may be added to your steam library with the following steps:
1) Download/install Dead Space on origin
2) Go on steam, click ADD GAME that's in the bottom left corner
3) Click ADD NON STEAM GAME
4) Find Dead Space and follow the rest of the steps