It's so easy to transfer a database from SQL Server 2005 to SQL Server 2008. Well the same holds good from SQL Server 2000 to SQL Server 2008. Read on...
Moving database from SQL Server 2005 to SQL Server 2008 in three steps
SQL Server 2005 can be migrated to SQL Server 2008 quite easily by manually detaching the database from SQL Server 2005 and attaching it to SQL Server 2008. This is a much easier process than the 'Copy Database Wizard' which has two procedures one of which is the same as the manual process but carried out under the watchful guidance of a wizard and the other which does not require the stopping of the Source server.