Setting Up Windows 7 as NTP Server

Here are the procedures on how to do it. It is the same as configuring the service for XP with only the last line added for the VMICTimeProvider.

Click Start, click Run, type regedit, and then click OK.
Locate and then click the following registry entry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\
In the right pane, right-click AnnounceFlags, and then click Modify.
In the Edit DWORD Value dialog box, under Value data, type 5, and then click OK.
Enable NTPServer.
Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer\
In the right pane, right-click Enabled, and then click Modify.
In the Edit DWORD Value dialog box, type 1 under Value data, and then click OK.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\VMICTimeProvider\
In the right pane, right-click Enabled, and then click Modify
In the Edit DWORD Value dialog box, type 0 under Value data, and then click OK
Exit Registry Editor.
At the command prompt, type the following command to restart the Windows Time service, and then press ENTER:
net stop w32time && net start w32time
To reset the local computers' time against the time server, run the following command on all the computers except the time server:
w32tm /resync /rediscover