I've had the privilege of meeting Jeremiah Grossman at a security conference. I'd recommend reading several of his white papers and then decide if you want to call his company up. I doubt they are cheap, but the best rarely is.
Does it not seem odd to you that the only competitor for Windows file sharing recommended here is a open source clone of the same technology they are trying to replace?
There is a reason why Windows servers are so popular and it is no one makes directory services, file sharing, group policy, and email/calendaring as easy as Microsoft. Microsoft has been so successful at creating these services and making them simple to administer that most open source projects try to emulate/replicate/duplicate what already has been done.
So stay up on your soap box saying how much better the open source version is...
Today is a good day for information-gathering. Read someone else's mail file.