Excellent article by Luka Manojlovic at http://luka.manojlovic.net/2011/06/24/windows-server-2008-2008-r2-ad-sync-with-external-ntp-server/ about configuring your Server 2008 to use the NTP Pool. If you are in the us you may use us.pool.ntp.org.
Thanks, Luka!