anon access to discussion group in FP

I have an IIS 6 server set up Windows 2003. Sites (subwebs) for my users are
protected by domain/username password in our organization for admin purposes
but anyone can browse the sites. Users edit the sites by opening the pages in
a browser, Edit With Front Page, enter username/password, etc.

I have a user who set up a discussion group via Front Page, including
selecting "Allow anyone to post comments" in the wizard however when someone
tries to do so, they are prompted for a network credential (which they won't
have).

How can I best solve this?

Thanks,

Sheldon