SQL Server 2000 and Security

Authentication is the process of validating that the user attempting to connect to SQL Server is authorized to do so. The authentication stage identifies the user by using a login account and verifies his ability to connect to an instance of SQL Server. If authentication is successful, the user connects to an instance of SQL Server. The user then needs permissions to access databases on the server. This is done by granting access to an account in each database, which is mapped to the user login.

The article continues at http://www.webknowhow.net/dir/Databases/SQL/070722sqlserver2000.html