Since SQL Server 2008 has been released, I find a lot of companies seriously considering the option to move their instances of SQL Server 2000 and 2005 databases to SQL Server 2008. However for a smooth upgrade, there are a couple of points that should be reviewed by a DBA, before carrying out the process. If you have already purchased SQL Server 2008 (SQL Server: How to Buy), then here are some important links from SQL Server Books Online to help you in the upgrade process:
Using Upgrade Advisor to Prepare for Upgrades - Upgrade Advisor is a tool that analyzes instances of SQL Server 2000 and SQL Server 2005 to identify known upgrade issues
Version and Edition Upgrades – A nice chart that shows all the upgrade paths to SQL Server 2008 from previous versions of SQL Server
Backward Compatibility - significant changes that might affect your applications after you upgrade to SQL Server 2008.
How to: Upgrade to SQL Server 2008 (Setup) - upgrade a stand-alone instance of SQL Server to SQL Server 2008
Hardware and Software Requirements for Installing SQL Server 2008 - the minimum hardware and software requirements to install and run SQL Server 2008
Some other important links that may prove helpful are:
Upgrading Business Intelligence Components
Let me know if there any other important links you can share and I will update this post.