Here a little news flash! Payday the Heist, will be free for download on October the 16th! To celebrate reaching 1.5 million members in their Steam group, Overkill Software is offering Payday: The Heist for free on October 16. So mark this date in your calendar and check the Steam community page for further instructions that day to obtain the game in Steam.
Then, when you have the serial, download the steambuild1 Wrapper (if you not already have it), and login into Steam and add the serial and download and play! Enjoy!