SharePoint 2010 cross domain authentication and authorization issue

Summary of the Intranet Set-up:-
• Internal Network: SharePoint Foundation 2010
• External Network: SharePoint 2010 (Full Version).
• Core Issue: External Entities are on a different network and do not have access to our Domain (i.e.) External Entities are not able to authenticate on to our EXAMPLE.COM domain.
• How we copy the Intranet from the Corporate Network over to the External Entities Network: Using STSADM we backup the Intranet on the Internal Server, Scheduled job to FTP across to the External Entities Server then Restores the site nightly.

External Entities Authentication Issue:
• The Internal version has network authentication (i.e.) single sign-on with our domain EXAMPLE.COM.
• The External Entities version has anonymous access enabled in order for External Entities Network users to see the copy of the Intranet. This is fine and allows External Entities users to see all content from the top-level but only down to the point inheritance is broken.
• On the internal version we have to break inheritance to set custom groups and permissions for editing. When we do this we give all Internal EXAMPLE.COM network users read access to that site to ensure they can still access the content.
• But for External Entities Users they can no longer access that content. They are now prompted to log in but because they can’t authenticate with our EXAMPLE.COM Domain so they can never access that content again once inheritance is broken from the top-level.

We tried various things but no success so far. (i.e.) create a local user on the Internal Server and External Entities Server with same user name and password. But SharePoint still prefixes the server name and ties to authenticate to the local user on the internal / corporate network.

Regards,

Rajesh

Rajesh Agravat