Clock synchronization Win xp Home

I have 2 PC’s that are clockin / clockout machines running XP Home Windows software. Is there a way that these PC’s could be synchronized to an atomic clock? They have access to the internet. Thanks for any ideas. I don’t want to pay upgrade price to win xp Pro software. I know they have a third tab when you display the calendar that allows you to do this. Any way to skin this cat will be appreciated.