PC clocks are notorious for being wrong; the hardware clocks drift, software clocks get interrupted when they shouldn’t, maybe the moon’s just in the wrong phase, who knows. A few seconds here or there shouldn’t hurt too badly, but they build up and get to bug people. There have long been time servers “out there” and the Network Time Protocol (NTP) has served well. Most PC users, though, haven’t heard of it or haven’t installed software to use it (I’ve used Tardis for years – recommended for folks who haven’t yet made the move to XP).
Windows XP has added it’s own synchronization bits – find the clock in your taskbar and double-click on it. You should have the normal Date & Time and Time Zone tabs, but now there’s a third Internet Time tab as well ~ or there may not be. According to XP’s own help: “If your computer is a member of a domain, your computer clock is probably synchronized automatically by a network time server. If your computer is not a member of a domain, you can synchronize your computer clock with an Internet time server.” Though the help says “probably”, TechNet article Q289689 uses a bit stronger language: “The Internet Time feature is only available in workgroup environments.”
If you’re part of a domain, then, you won’t see a third tab – you’re expected to get your time sync’d from your domain server. That’s a good thing; then only the domain controller(s) need to bother the “master” time servers. If your system admin doesn’t have this already happening automatically, you can use Start->Run net time /set /yes to sync manually (or use Start->Run cmd then enter the same command to read any messages or errors).
For everyone else, back to that third tab. Just make sure the “automatically synchronize” box is checked and pick a server (it really doesn’t matter which; they’re all sync’d with each other). Click the “update now” button. You may have trouble if the date on your computer’s wrong, or if you’ve got a firewall, or of course if your system’s not connected to the Internet, but otherwise your clock should be reset. And every week it’ll happen again.
Network Administrators – see also What Time Is It, Redux for NTP Server on Windows 2000 or 2003.