Вообще-то существует небольшая утилитка, NTSwitch она называется.
Описание (переводить лениво, но, думаю, и так все ясно):
This program will change the operating system type on your computer. You can turn a Windows NT Workstation (or a Windows 2000 Professional) installation into a Server environment and vice versa.
The software also appears to turn Windows XP Professional into "Windows Whistler Server", but the resulting operating system is not fully functional. DO NOT USE THIS PROGRAM ON WINDOWS XP UNLESS YOU ARE WILLING TO REINSTALL THE OPERATING SYSTEM.
REASON: It's a well-known fact that Microsoft's Windows Workstation and Windows Server products share the same binaries - the only difference lies in the registry. The sole reason for the creation of this software is to demonstrate this fact to the public.
Если кто захочет попробовать, могу выслать на мыло - zip-архив ~100 кило. Адреса шлите в ПМ.