What kind of error are you getting?

The browser  tries to load the page for very long time
and finally gives "No page to display". This happens
after you enter the credentials in the window
authentication dialog.

Even we have been trying to resolve this firewall
authentication error without much success..
We followed all the procedures mentioned in the
white paper for extranet deployment and also made use
of the tool that automates this process. This set
works fine when the site  is accessed  from outside the
firewall.
However when the site is accessed from a machine
behind the firewall  the following happens-->
1) It first asks for a firewall authentication ID.
2) Once authenticated it asks for the domain
authentication for the domain  in which the SPS server
lies.
3) After giving the proper account we get a
HTTP 403
Forbidden access  error..

We have been trying to resolve this problem  for a long
time now...