Hi Keith, just for the record, I don't think that's very clear in the instructions. I downloaded it from the download link on Bundle and it came with a read-me that said this:
For the DRM-free version of the game, all you have to do is register your Steam or Desura key at http://www.arcengames.com/ and it will give you the DRM-free version's CD key.
So that had me, and apparently quixian, and likely others scrounging arcengames.com trying to find where to put in our steam or desura keys.
I put it into Steam and it works for me now, so I don't have an issue, but I just thought I should let you know. I'm glad I found this thread; thanks for your post explaining what to do.