Copy database schema from SQL Server 2008 to SQL Server 2005
If you aren't using any SQL2008+ only features (e.g. compression) you will be able to script out the objects you require and execute in SQL2005. If you're not sure if any SQL2008+ features are in use, trial and error (script and execute, see what happens) will soon tell you where the problems are.

This is very different to restoring a backup from 2008 to 2005, which is not possible.