The newest version of OS X, Snow Leopard (10.6) has time zone automatically function built into the OS.
To enable thisGo to System Preferences
Select “Date and Time”.
Select the “Set time zone automatically by location” option.This works using CoreLocation, just like the iPhone. Even though it’s just an option. Once you do this, your time zone will change as you travel.
Date & Time Panel tags: Date and Time
, system preferences
, time zone