Please go check the SharePoint Team Blog, you must do this! I will update my step by step with the extra steps later today! They change a setting either in the DB or registry that sets your image to "Eval" status. After applying SP2 your SharePoint will expire in 180 days! Yikes!
http://blogs.msdn.com/sharepoint/archive/2009/05/21/attention-important-information-on-service-pack-2.aspx
Chris