http://www.sqlservermart.com/HowTo/MSSQL_Convert_2008_To_2005.aspx
Requirements
If you are trying to restore database backup of SQL Server 2008 to SQL Server 2005, you are bound to fail. Database backup of SQL Server 2008 is not compatible backward, you cannot restore it to SQL Server 2005. The following is a solution to convert databases of SQL Server 2008 to 2005
Step by Step Guide
1) Start convert wizard
Open SQL Server Management Studio2008. in 'Object Explorer', right click the database that you want to convert. Select 'Tasks' > 'Generate Scripts...'.
2) Next
Click 'Next'.
3) Select database and objects
Select the database that you want to convert, and check on 'Scripts all objects in the selected databases'
4) Convert Options
Set options:
'Script for Server Version' = 'SQL Server 2005'
'Script Data' = 'True'
'Scirpt Database Create' = 'True'
5) Output Option
Select option 'Script to file', 'Single file' and 'Unicode text'.
6) 'Finish'
View summary and click 'Finish'.
7) Result
Now you got a complete database creation script with data. It can be executed on target database server.
8) Amend Script
Open the generated script in SQL Server Management Studio 2005. Find the following section and amend the path to proper data folder
CREATE DATABASE [StockTraderDB] ON PRIMARY ( NAME = N'StockTraderDB', FILENAME = N'c:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\StockTraderDB.mdf , SIZE = 4352KB , MAXSIZE = UNLIMITED, FILEGROWTH = 1024KB ) LOG ON ( NAME = N'StockTraderDB_log', FILENAME = N'c:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\StockTraderDB_log.LDF', SIZE = 6272KB , MAXSIZE = 2048GB , FILEGROWTH = 10%)
9) Execute the Script
When finished, You should get converted database of SQL Server 2005