[eyedigress]

http://en.wikiquote.org/wiki/James_Madison

It seems to be real. Make sure your Christmas Card is with blessing.

[Huck]

No, actually it is bogus. Apparantly even Barton said so. From your link:

Attributed to Madison in The Myth of Separation Between Church and State (1989) by David Barton, he has since declared it a misattribution, after Madison scholars reported that this statement appears nowhere in the writings or recorded utterances of James Madison.[12]

So, that settles it. If the author himself admits it's bogus, I think the discussion is pretty well settled. And since the author has fessed up to it, I guess I can include a blessing in that Christmas card.