There is a new Windows SharePoint Services 3.0 SDK April 2007 Revision available.
Site: http://msdn2.microsoft.com/en-us/library/ms441339.aspx
Download SDK: http://www.microsoft.com/downloads/details.aspx?familyid=05e0dd12-8394-402b-8936-a07fe8afaffd&displaylang=en
Additional Resources
Official
SharePoint: http://blogs.msdn.com/sharepoint/
Enterprise Content Management: http://blogs.msdn.com/ecm
Forum: http://forums.microsoft.com/MSDN/default.aspx?ForumGroupID=328&SiteID=1
Discussion Groups: http://www.microsoft.com/communities/newsgroups/en-us/default.aspx?dg=microsoft.public.sharepoint.portalserver
More
SharePoint Blogs: http://www.sharepointblogs.com/
WF + SP2007
http://www.developer.com/net/net/article.php/3652346
http://blogs.msdn.com/sharepoint/archive/2006/12/01/developing-workflows-in-vs-part-7-summary-and-final-thoughts.aspx
