This is one of the best article to read about Tools and approcaches to upgrade production servers to SQL Server 2008.
SQL Server Technical Article:Performing an upgrade is a complex and often risky project. A successful upgrade can provide an organization with a modern platform for development and production. An unsuccessful upgrade can cause lost time and money, and it can create a bad perception for the future.
This paper documents approaches and tools that can help DBAs and developers to achieve successful and mostly painless upgrade of SQL Server databases from Microsoft® SQL Server® 2000 or SQL Server 2005 to SQL Server 2008 (or SQL Server 2008 R2).
In the methodology this paper discusses, a SQL Server workload is captured on customer production environment, and then this identical test workload is run on the old and new versions of SQL Server in a test environment to compare performance and isolate any problem queries. For this approach, we use components from the "RML Utilities for SQL Server" set of tools.
Source : http://msdn.microsoft.com/en-us/library/ff758640.aspx