Settings for daylight saving appear to be stored in binary form in the file pointed to by the symbolic link /etc/localtime (on Debian anyway, on another distro I see /etc/localtime already contains the binary data). In my case the actual binary file is
The page http://www.twinsun.com/tz/tz-link.htm
gives some explanation of where this stuff comes from. I looked at the TZ database referenced there and it already has the recently announced one-off daylight saving extension for the 2006 Commonwealth Games in Melbourne. I'm not sure how fast this propagates into new linux distributions. I guess you can DIY by building the 'compiler' to turn the human-readable timezone data in the database into the binary file for your timezone.
I have a feeling older UNIX systems may have used a simpler mechanism using numerical info in /etc/timezone, which now just contains the name of the the time zone, if it exists at all.
Are you set to UTC or local time? On a Debian system this is set by a line in /etc/defaults/rcS. All time related stuff works much better on UTC - especially daylight saving, using ntp to set the clock accurately, logging in from a different timezone or moving your computer across time zones.
There is a good guide (Debian specific, but lots of general info also) here
I had a closer look at the timezone info and created a new binary file for my zone. Just download the tzdata and tzcode files, unpack them into a new empty directory and run 'make'.
This gives (among other stuff) an executable 'zic'. Running this on the (human-readable) australasia data file gives several new directories with binary zoneinfo files, including Australia/Sydney. Command 'zic -d . australasia' generates these in the current directory. Result was same size as original but 4 bytes were different.
So it looks like you can update your zoneinfo with something like
zic -d <your zoneinfo dir> australasia
(as root, and with your region data file). Maybe I should reboot sometime between now and the Commonwealth Games