From Mark Harrison's blog:
The SharePoint Server 2007 area on the Office Developer Center has gone live – this provides community resources and up-to-date announcements. It will contain information about planning, coding, building, deploying, and migrating solutions for SharePoint Server. Includes the SharePoint Server Migration Center addressing the issues of migrating SharePoint Portal Server 2003 and Content Management Server 2002 to the new common architecture.Also checkout the Windows SharePoint Services Developer Center.
You can find this article here.