From Paul Andrew's blog here.
The BizTalk Adapter for Windows Workflow Foundation SDK Sample (June 2007 CTP) is a preview of some new technology for business logic and process developers. It provides for workflow models developed using Windows Workflow Foundation from the .NET Framework 3.0 to be hosted in BizTalk Server 2006. By doing this the workflow gains access to services from BizTalk Server 2006 including scalability, reliability, manageability, and access to messaging with BizTalk Server ports. The next major version of BizTalk Server is planned to be built on Windows Workflow Foundation and this CTP provides an option for customers to do this with current technologies. A release date has not yet been planned and will depend on customer feedback and the sample is currently not planned to be Microsoft supported. The CTP is suitable for software developers familiar with Windows Workflow Foundation and is provided as an SDK sample with source code.
The sample provides a tool that evaluates an existing WF workflow model and creates a BizTalk orchestration project as a proxy for that WF workflow model. The orchestration can then be deployed to BizTalk Server and the WF model is used.