As you have probably already heard, the Federal Government has changed the start and end dates for Daylight Savings Time. Most computers will need a small update to correctly adjust for these new dates. Apple has released their update for Mac OS X today. You can download this using Apple's built-in Software Update service.
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.Windows update information can be found in February 2007 cumulative time zone update for Microsoft Windows operating systems
For more information about this update, see http://docs.info.apple.com/article.html?artnum=305056