On the Builder.com.au website today, there's a quick new tutorial on grabbing the correct time for a user's "home" rather than the server's time.
PHP comes with an extensive catalog of date and time functions, all designed to let you easily retrieve temporal information, massage it into a format you require, and either use it in a calculation or display it to the user. However, if you'd like to do something more complicated, things get much, much hairier
To make things easier, they enlist the service of the PEAR Date package to help bridge the gap between the time zones faster. They give some of the basics of using the package before actually getting into the time zone conversion. The code is pretty straight-forward and they even include other simple tips like how to calculate the GMT offset and how to add and subtract timespans.