From LedHed's Wiki
Windows 2003 & XP
Stop the Windows Time service
net stop w32time
Force a resync
w32tm /resync
Set the time source
net time /setsntp:<Time_Source>
View the current time source
net time /querysntp
Note: In most cases you dont need to stop the w32time service anymore.
Windows 2008 Server
Stop the W32Time service:
net stop w32time
Configure the external time sources:
w32tm /config /syncfromflags:manual /manualpeerlist:â0.pool.ntp.org, 1.pool.ntp.org, 2.pool.ntp.orgâ
Make your PDC a reliable time source for the clients:
w32tm /config /reliable:yes
Start the w32time service:
net start w32time
The windows time service should begin synchronizing the time.
Check the external NTP servers in the time configuration by typing:
w32tm /query /configuration