After several months of work, we're pleased to announce publication of a new whitepaper: Upgrading SharePoint Portal Server 2003 Customizations to SharePoint Server 2007.  To view the whitepaper visit: http://msdn2.microsoft.com/en-us/library/bb954662.aspx or http://blogs.msdn.com/joelo/archive/2007/11/06/upgrade-customization-articles-posted.aspx for additional details.