Any trust relationships between the domains? Are they in the same forest?

I don't see how a user obtains access to any server, let along an SPS
server, if they can't authenticate somehow at the server  or at a trusted
source.

Our portal is mainly an integration of applications. users  have to
pass a corporate SSO to gain access to the portal. We plan to deploy
the portal itself using anonymous mode, so that users can access the
portal and the applications as long as they have corporate SSO
accounts.

No SPS/WSS user accounts  are really needed to achieve the above
requirements. However, SPS/WSS user accounts are needed when
personalization and othe SP features come into the picture. Thus, we
have to find a way to enable all the user accounts from different
domains.

I think this is a windows domain  administratration question. Any
further suggestions are highly appreciated.