discussion group post problems

Using server 2003 frontpage 2003 and server extensions.

I am using a discussion group created through frontpage. The person needs
to log in to be admitted to get to the discussion area. When they try to
post a message they get another log on box. In the folder properties the
users have read & execute, list folder contents, read and write all
selected. In IIS the rights are read, write, log visits and index this
resource.

Is there something missing that is not allowing users to be able to post?