[MichaelCrawford]

Reverse engineering for interoperability is really quite common. I myself reverse engineered the Movie Magic Scheduling database format under contract to Graphical Planet in 1998. I had that on my resume until quite recently; no one ever gave me any grief over it.

However there are some specific legal requirements, as were detailed by the primary author of Samba, which enables one to mount and to serve Windows SMB/CIFS shares from *NIX systems. He covered those requirements at Advogato:

http://www.advogato.org/article/302.html

Note that the author advises that you buy a lices for that very expensive piece of software.