Mac OS X Server is a retail product. It is a server operating system with a Macintosh-like Graphical User Interface (GUI).
Darwin OS is the Open Source release of the Mac OS X Server operating system foundation. It does not include source code for the graphical user interface, NetBoot, Macintosh Manager, Apple File Services or WebObjects. Darwin OS is available from Apple at
http://www.apple.com/darwin/
Apple does not offer telephone technical support for Darwin OS components.