Upon upgrading from OS X 10.0.4 to OS X 10.1 some users might experience that they can't set the time zone. The fix is to open a terminal and type:
sudo rm /var/db/TimeZone.cacheThen log out and log back in and you should be able to change your time zone.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010929103351102