The Windows Server 2003 Customer Preview Program site is now online. What is Windows Server 2003 R2? From the FAQ:
Windows Server 2003 R2, an update release of the Windows Server 2003 operating system, makes it easier and more cost effective to extend connectivity and control to identities, locations, data, and applications throughout and beyond your organization.
Here's a link to the new page with information about getting the preview:
Windows Server 2003 R2 Customer Preview Program
Be among the first to experience the upcoming version of the Windows Server operating system, which helps you extend connectivity and management throughout your organization.