There is a great set of white papers, reference documentation and training samples that has been recently made available for the recently released Windows Server 2008. First of all, you can download a 248 pages long "Windows Server 2008 Reviewers Guide" that provides a great infra and dev view of this new Microsoft platform. Get it here. Then there is the long awaited (at least by me) Windows SDK for Windows Server 2008 that you can download here. Finally you might be interested in downloading the Windows Server 2008 Developer Training Kit from here. The training kit is based on the DinnerNow application that you can get from here.
Source:→ Stefano Mapelli's weblog
Windows Server 2008, Win2K8, Windows Server, WS2008, Developers, Knowledgebase, Guide