The Daylight Saving Time Update for Mac OS X and Mac OS X Server addresses recent changes in the way Daylight Saving Time will be observed in the U.S. and Canada beginning in March 2007 and includes the latest time zone information for the rest of the world.
That article links to this one:
Apple is providing software updates for Mac OS X 10.3, 10.4 and later based on worldwide time zone information available as of January 8, 2007. To make sure that your clock maintains the proper time, simply install the updates that are shown for your computer in Software Update. You should install these updates even if your computer is used in a time zone that is not affected. For more details about the available updates, or if you have an earlier Mac OS version, see below.
The 2007 time zone and Daylight Saving Time rule changes for the United States and most of Canada are already available in Mac OS X 10.4.5 or later.
If you’re still using Mac OS X 10.2.8 or earlier, you can adjust your clock manually using Date & Time preferences. Deselect the option to set date and time automatically, then set the time for your local time zone as needed.
Still using Mac OS 9.2? Use the Date and Time control panel to deselect the option to observe Daylight Saving Time changes automatically, then enable Daylight Saving Time manually. Applications that run in the Classic environment of Mac OS X will honor the Daylight Saving Time setting in Mac OS X.
Applications that run in Classic will honor the Daylight Saving Time setting in Mac OS X.
Glad we could clear that all up.