Just a followup to my earlier post on updating FreeBSD to handle the changes in Daylight Savings Time starting in 2007....
There are a couple mentions ,  on the freebsd-stable mailing list that the
/etc/localtime file is binary compatible across various versions of FreeBSD.
This means you only have to get one good copy of
/etc/localtime for your timezone, either by pulling from a FreeBSD 6.2 or higher machine, or installing the
misc/zoneinfo port on one older machine and run
tzsetup. Once you have that good version, you can copy it around to your other FreeBSD boxes, regardless of what version they're running.
This seems to also work between FreeBSD and OpenBSD (and perhaps Net and Dragonfly). I had a single OpenBSD 3.7 machine I wanted to update, and it seems to work OK to use a
/etc/localtime pulled from a FreeBSD box. On OpenBSD (3.7 at least),
/etc/localtime was a symlink to a file in
/usr/share/zoneinfo/. I just removed the symlink and made a new one pointing to a new timezone file I stuck somewhere on the disk. Checking for the correct DST dates in OpenBSD seems to be the same as with FreeBSD:
zdump -v /etc/localtime | grep 2007
Look for March 11th as the start date.