If you are running Windows XP, you'll never have to worry about manually setting your computer's clock again!
Just double-click the little clock in the System Tray and it will bring up the Time and Date Properties screen. Click the Internet Time tab and you'll see a button that lets you instantly synchronize your clock with one on the internet. Of course, you have to be online for this little trick to work.
Also, you'll notice that there's a check box on that screen that says "Automatically synchronize with an internet time server." If you uncheck that box, you won't be able to do a manual synchronization as described above. However with this feature enabled, not only can you do our little trick, but your computer will automatically update its time once a week - all by itself.
Of course, you need to be online when it's time for the synchronization in order for this to work.
Anyhow, no matter how it gets updated (manually or automatically), it's still a handy way to keep your computer's clock right on time.