Hi sherow,
DCpromo is a windows server operation system command which is used to promote / make normal windows server functionality to server functinaity as domain controller. A domain controller can manage almost all resources in you network such as users
,PCs, Printers and etc. However, Client Operation System such as Windows 2000/XP/Vista/7 are just an operating system for normal user, it doesn't assume the role of the server.
What is Domain Controller Roles
http://technet.microsoft.com/en-us/library/cc786438(WS.10).aspxThere is an amazing pack of free network admin tools.
click here to download it