I saw this over on Hardforums.

Cryostasis Code Giveaway!
Goto this website http://www.evga.com/code/default.asp and claim your code.

Then, you go to the link - http://store.nvidia.com

Click add to cart, fill out the info, apply the promo code, if it doesn't work try another one, etc.

It'll eventually work, you click "begin download". It'll download a manager, run the manager and it'll start downloading Cryostasis. You can then launch it like any other game.