Update Computer Clock Through a Firewall

[cscgal]

I found this in a few different places around the 'net - hopefully it's helpful:

Update Computer Clock Through a Firewall

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.

However, the Internet Time service in its default state does not work with Internet Connection Firewall enabled on a dial-up connection in Windows XP. Click Start, point to Connect to, and then click Show all connections.
Right-click your dial-up account, and then click Properties.
On the Advanced tab, click Settings.
Click the Add button, and type Internet Time Service for the description.
Enter 127.0.0.1 for the IP address, and enter 123 for both the External and Internal port numbers, and then make sure that TCP is selected.
Click OK three times until the Properties dialog box closes.
If you?re online, a message box tells you that you need to disconnect and reconnect for the settings to take effect. When you double-click the clock on the taskbar, and then click Update Now on the Internet Time tab, your clock will be synchronized with an Internet time server.