Message Board/Forum with Automatic Log In (Authentication/..

Hi there,

I'm developing an intranet, on which I'd like to include a staff
forum/message board (it has to be an ASP one).

I am currently doing some investigation into which forum would be best
suited to our needs. We'd like to have users automatically logged into
the forum, i.e. their Windows username will be used, presumably using
Active Directory. We are using Windows Server 2003 SP1.

I've already looked at Snitz and Web Wiz, but it appears that
developers ran into problems when trying to implement automatic log on.

Can anyone tell me of such a message board that supports what we'd like
to do? Any help would be greatly appreciated!

Best Regards,
Stewart.

PS Being a charity, we'd prefer to have a free one if possible!