How to downgrade a SQL Server from 2008 R2 to SQL Server 2005?
Here's the situation. You have done an in-place upgrade of SQL Server from 2005 to SQL Server 2008 R2 and you do not have any backups for 2005 version. (This was one of the interview questions I faced)
You can achieve this by Right click the database, go to 'Generate Scripts', Advanced, 'Script to Server Version' option.
If the db is too large, script out just the database structure, then use your favorite method (SSIS, BCP, Import Wizard) to push the data.
-Karthik (Database Consultant)