Setting up a Unix system to be an NTP client is generally straightforward. On those Unix platforms that include NTP in the default configuration, you may only need to make a few adjustments to NTP’s ...
IIRC windows doesn't run ntp by default, it runs some propretary w32time service instead. I think it has an ntp client built in, but I'm not sure if it can be an NTP server out of the box.