Windows does have a feature that tries to synchronize the clock with a server on the Internet, but it does not synchronize often enough, in my view.  And if it fails when it attempts to synchronize, your PC's clock can get way out of wack.

For some reason, Windows makes it impossible to control how often the clock gets synchronized.  Probably to avoid a massive traffic problem on the time server.

But today I found a nifty little program that lets you change the synchronizing to occur either daily or hourly.

I think hourly may be a bit overkill, but daily is definitely a good idea.

Here's a link to the utility: http://www.dougknox.com/xp/utils/xp_inet_time.htm

It comes in a simple zip file, and there is no installation necessary.  The zip file contains one file.  Just copy that file to wherever on your hard disk you'd like to keep it, and then run the program.

It displays a little dialog box asking how often you'd like to synchronize the clock.  You click the option, click Apply, and the click Exit.  That's all there is to it!

Works with Windows XP and Vista.  I haven't tested Windows 7 yet, but it probably works there too.