The SQL Server 2008 Upgrade Technical Reference Guide has been designed to achieve a smooth transition, and emphasises the need for sufficiently planning for the upgrade. This 490 page document covers the essential phases and steps involved in upgrading existing SQL Server 2000 and 2005 instances to SQL Server 2008 by using best practices. These include preparation tasks, upgrade tasks, and post-upgrade tasks.
It gives an overview of the technical issues and decisions that are involved in an upgrade to SQL Server 2008, as well as recommendations for planning and deploying an upgrade. It also contains a table of allowed SQL Server 2008 version and edition upgrade paths, as well as an upgrade planning checklist.