net help time:
[\\computername | /DOMAIN[:domainname] | /RTSDOMAIN[:domainname]] [/SET]
NET TIME synchronizes the computer's clock with that of another computer or domain, or displays the time for a computer or domain. When used without options on a Windows Server domain, it displays the current date and time at the computer designated as the time server for the domain.
\\computername — Is the name of the computer you want to check or synchronize with.
/DOMAIN[:domainname] — Specifies to synchronize the time from the Primary Domain Controller of domainname.
/RTSDOMAIN[:domainname] — Specifies to synchronize with a Reliable Time Server from domainname.
/SET — Synchronizes the computer's time with the time on the specified computer or domain.
(Sorry, it's from Windows 7, but the general workings and options are the same for XP.)