Oops , typo in question. It should say the application team would now like to go back to SQL Server 2000 without data loss.
Moving from SQL 2005 to SQL 2000 isn’t quick or easy. There is no way to restore a SQL 2005 database to a SQL 2000 database. You will need a decent outage window to move the data.
You can try the copy database wizard. If your database isn’t that complex it may work for you.
If the database is to complex for the wizard you will need to script out all your objects then import the data using the import/export wizard or by manually creating a DTS/SSIS package.
I’m curious, why the move back from SQL 2005 to SQL 2000?