Well, the first answer that comes to mind is to look at the time on them and
see if it is the same!
However, that's probably not what you want to hear.
Look in the System Event log for errors from the time service.
Look at the registry values at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters\
if the Value called "Type" is set to
- "NT5DS", this means that the computer is a member of a Windows 2000 or
2003 domain and is set to sycnhronize time with the Domain Controllers
- "NTP", this means the computer is configured to synchronize time with
the time source specified by the registry value "NtpServer" under the same
Key
To change the settings, use the the w32tm /config command (use w32tm /? to
see the functions and parameters).