In Windows XP you can get to the 'Internet Time' settings (to select a ntp server or force an update) via the 'Date and Time Properties' in Control Panel.
Anyone know where this is found in Windows 7?
As pointed out, I won't be able to do this if attached to a domain.
My problem was that my PC was trying to sync with 'time.windows.com' which is blocked by out firewall. In the end I changed the registry key (
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\DateTime\Servers) to point to our internal ntp server and the time is now syncing fine.
(I know that domain computers should sync with their domain controllers but this machine is not actually logged in to the domain most of the time.)