Well, we've finally been able to get it posted! The SAFE Signing Interface for Office 2007 has been posted to Codeplex, with the source code for the interface being posted shortly.
The installation executable, along with installation instructions, is now available at http://www.codeplex.com/safe.
We are also releasing the source code into open source - available on the same site - and to be available as soon as we can get it uploaded.
Look for another posting here to that end!
While this is a reference implementation (and thus, unsupported), we are hoping that the broader community will take up the support for this important capability, extending it as the SAFE standard is extended. If you are interested in participating as a developer on this project, please send me an e-mail at firstname.lastname@example.org