In the early 1990s, Microsoft and IBM worked jointly to develop OS/2, but the relation-ship turned sour. Microsoft and IBM split up and went separate directions, with Microsoft later releasing Windows NT in July 1993. Microsoft's server line as we know it today finds it roots in these humble beginnings. Windows NT was the professional version of the operating system targeting company and government organizations.
Windows NT created the foundation for the desktop market with Windows XP Home and Windows XP Professional. Windows XP Professional contains superior networking and security features over the Home edition and now is used widely.
The server market went from Windows NT to Windows Server 2000 in February 2000. April 2003 saw the introduction of Windows Server 2003, which then was replaced with Windows Server 2003 Release 2 in December 2005. Windows Vista and Longhorn are under development and will replace Windows XP and Windows Server 2003.
What this means for the auditor is that there are many versions of operating systems in most large environments. It's highly recommended to find the time to familiarize yourself with the operating systems in your particular situation. Not all utilities will work on all systems. In some situations, hosts exist on your networks that are no longer supported by Microsoft. Additional controls should be in place to protect these systems, such as technologies that prevent network attacks or malware propagation.
Significant background information is documented online covering the development of the Microsoft platform. For example, check out any search engine and type "Micro-soft History" into the search box. Select "Search," and you will find an abundance of information about the current and future development of the Windows platform.