When you attach a SQL Server 2000 into a SQL Server 2012 instance directly, you will get error:
Error: failed to attach db - Database 'DB_99174A_Jebon' cannot be upgraded because its non-release version (539) is not supported by this version of SQL Server. You cannot open a database that is incompatible with this version of sqlservr.exe. You must re-create the database.
Databases created on SQL Server 2000 or with compatibility level 80
cannot be attached to SQL Server 2012 because they are incompatible with
this version of SQL Server.
The database can be attached (migrated) first to a SQL Server 2005,
SQL Server 2008 or SQL Server 2008 R2 instance, then detached and later
attached to the SQL Server 2012 instance.