This is an another update to the Microsoft Dynamics CRM 4.0 SDK. You can download it here or check on the CRM Developer Center in a few days.

The Microsoft Dynamics CRM 4.0 Software Development Kit (SDK) is for developers, system customizers, and report writers.
It contains all new information about creating plug-ins, working with custom workflow activities, using the new Web services, using new data management features, and much more.

This SDK contains information for developers writing server side code, custom business logic, integration modules, workflow assemblies, and more. It provides an architectural overview of Microsoft Dynamics CRM, the entity model, security model, and Web services. Sample code and walkthroughs guide you through the new features.

Download details : here