Windows Server 2003 R2 RC 0 is available for download. You can get more information here:
Windows Server 2003 R2 Release Candidate 0
Try Windows Server 2003 R2 RC0 today and extend your connectivity and control to data and applications throughout and beyond your organization.
This page contains links to information about new features, a reviewer's guide, a FAQ, and a product overview. There's additional infomation available on the TechNet Windows Server 2003 R2 Beta Roadmap page.
This is the introduction from the Product Overview page:
Windows Server 2003 R2 is an update release of the award-winning Windows Server 2003 operating system. Built on Windows Server 2003 with Service Pack 1 (SP1), Windows Server 2003 R2 takes advantage of the stability and security of a proven code base while extending connectivity and control into new areas. Windows Server 2003 R2 offers all the benefits of Windows Server 2003 SP1 while greatly improving branch office server solutions, identity and access management, storage setup and management, and application development inside and outside your organization's traditional boundaries. Windows Server 2003 R2 is easy to integrate into an existing Windows Server 2003 environment as it has the same application compatibility, manageability, and serviceability as the existing servers with SP1.