If you have an Alternate Access Mapping configured for a MOSS 2007 site with Integrated Authentication you might find that you get prompted for the DOMAIN\UserName and Password. After 3 attempts you get to a HTTP 401 error.
This can be resolved by following the steps in MS KB 896861
HTH,
Sam
7d41ee08-e877-457f-b346-736c70f1f8e2|0|.0
MOSS, IIS
moss, alternate access mapping, http 401, authentication, failed