I'm facing an annoying problem on my SPS installation.
On my company, the web servers and database servers are located on separated domains. These two domains don't have trust relationships between each other.

So I've created a user account named usr_spsadmin on both domains with the same password. This user is a member of the Power Users group on the web servers and is assigned Security Administrators and Database Creators on SQL Server.

This user account is set to be used for administrative operations that create, modify, or grant access to the configuration or portal site databases. It is also used as the Default Content Access Account and the Portal Site Application Pool Identity.

The problem is when I try to create the configuration database I get the following message:
Error accessing database. Verify that the database server name and the instance name (if present) are correct. Also, ensure the configuration database administration account has sufficient permissions on the server or instance and the service corresponding to your SQL Server instance is running.

It seems it cannot authenticate the user. If I click OK again it manages to create the configuration database (miracle?). But when I try to join other servers to the server farm, using the Connect to Existing Configuration Database option, I get "Unexpected error ocurred" and no connectivity.

Do you have any ideas on how I can acomplish that?