"Enable Internet Time Services behind Windows XP Personal Firewall:

The Internet Time service in its default state does not work with the Windows XP Personal Firewall enabled on a dial-up connection.

To re-enable this ability while maintaining your firewall follow these steps:

Go to My Network Places, and in the Network Tasks sidebar select View Network Connections. Right-click your dial-up account and select Properties. Click the Advanced tab and click Settings.

Click Add and enter "Internet Time Service" for the description. Enter 127.0.0.1 for the IP, and enter 123 for both the External and Internal port numbers and select TCP. Click OK until the Properties box disappears.

If you are online, a dialog box will appear telling you that you need to disconnect and reconnect for the settings to take effect.

Now when you double-click the system tray Clock and select Update Now from the Internet Time tab, it should work correctly."