I saw these downloads passing by when I was checking my mails.

  Windows
SharePoint Services 3.0 SDK

This SDK contains conceptual overviews, programming tasks,
samples, and references to guide you in developing solutions based on
Microsoft Windows SharePoint Services 3.0.
  Microsoft
Office SharePoint Server 2007 SDK

This SDK contains conceptual overviews, programming tasks,
code samples, references, and an Enterprise Content Management starter kit to
guide you in developing solutions based on Microsoft Office SharePoint Server
2007.