Ntpd assistance

[alden.pierre]

/etc/rc.conf contains the following:

ntpdate_enable="YES"
ntpdate_flags="timex.cs.columbia.edu"
xntpd_enable="YES"        # Run ntpd Network Time Protocol

/etc/ntpd.conf contains the following:

driftfile    /etc/ntp/drift
server 65.211.109.1
server 65.211.109.11
server 209.51.161.238
server 128.59.59.177


Am I doing something wrong here?  My time seems to go out of sync after 
my FreeBSD 4.10 box has been up for a couple of hours.  Any help would 
be greatly
appreciated.

Thank You
Alden Louis-Pierre