According to an official post in the Dark Souls: Prepare to Die Edition Steam forums, the migration from GFWL (Games for Windows Live) to Steam has been delayed until December.
More information.Attention Dark Souls fans!
- UPDATE 11/25/14 -
We are working hard to finalize the process to move your Dark Souls: Prepare to Die saves and achievements to Steam. We need to conduct additional testing and we are now targeting December to begin this process. We'll have more information in the coming weeks. Thank you very much for your patience!