How to restore a database from SQL Server 2000 to SQL Server 2012
SQL Server 2012 no longer supports restoring SQL Server 2000 databases. You need to take an intermediate step:


backup your SQL Server 2000 database
restore it to SQL Server 2005 / 2008 / 2008 R2
change the compatibility level to at least "90" (SQL Server 2005)
backup again from that intermediate server
then restore that second backup on SQL Server 2012


Or depending on size and complexity of your SQL Server 2000 database, it might be easier to just script out the structure and data into SQL scripts and then run those on SQL Server 2012.