NTP for Windows operating system
Windows Time Service uses a version of NTP, normally a simplified version, of the Internet protocol which is designed to synchronise machines on a network. All versions of Windows Server since 2000 have included a time synchronization facility, called w32time.exe
Microsoft Windows 2000 has a time synchronisation utility built into the operating system called Windows Time (w32time.exe) which can be configured to operate as a network TimeServer. Microsoft and others strongly recommend that you configure a TimeServer with authentication
An easy to follow manual to set ntp on windows 2003 server (applicable to other windows versions). External time source is easily configurable to supply accurate time for NTP Windows machines.