How to Setup a Windows 2008 R2 SNTP/NTP Server

source: http://bchavez.bitarmory.com/archive/2009/12/21/how-to-setup-a-windows-2008-r2-sntp-ntp-server.aspx

Gee, setting up an SNTP/NTP server in Windows is not intuitive.
The good news is: When configured correctly, you can use the Windows Time (W32Time) service as an SNTP/NTP server for both windows and non-windows SNTP/NTP clients.
Here's how to do it:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry entry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\
   
3. In the right pane, right-click AnnounceFlags, and then click Modify.
4. In the Edit DWORD Value dialog box, under Value data, type 5, and then click OK.
5. Enable NTPServer.
   1. Locate and then click the following registry subkey:
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
                                                      Services\W32Time\TimeProviders\NtpServer\
   2. In the right pane, right-click Enabled, and then click Modify.
   3. In the Edit DWORD Value dialog box, type 1 under Value data, and then click OK.
6. Exit Registry Editor.
7. At the command prompt, type the following command to restart the Windows Time service, and then press ENTER: net stop w32time && net start w32time
   

This should get you setup with minimal registry hack impact.

Tips

• Make sure W32Time is set to Automatic startup mode.
• Make sure UDP 123 is allowed through your firewall.
• Use this InternetTime program to help you debug connectivity to your SNTP/NTP server.
  internettime.zip