These have a lot of cool new stuff and this version reflects the feature enhancements that are part of the recent Infrastructure Update! If you download the MOSS SDK, that's all you need. Remember to uninstall previous versions. Go get'em.....
MOSS SDK v1.4
WSS SDK v1.4
Also, bookmark the online MSDN libraries:
Windows SharePoint Services 3.0 SDK
Microsoft Office SharePoint Server 2007 SDK