Just released SharePoint SDKs; these look quite meaty -- The wss one weights in at nearly 34MB, compressed.
Windows SharePoint Services V3: SDK
This SDK contains conceptual overviews, programming tasks, samples, and references to guide you in developing solutions based on Microsoft® Windows® SharePoint® Services (version 3).
SharePoint Server 2007: SDK
The Microsoft Office SharePoint Server 2007 (Beta) SDK contains conceptual overviews, programming tasks, code samples, and references to guide you in developing solutions based on Microsoft® Office SharePoint® Server 2007.
I've also just installed the fresh Beta 2 releases on a virtual machine, so I'll be looking forward to porting my PowerShell SharePoint provider to v3...