arche

Hi, part of a small member system I am creating for my site allows users to change their timezone, then all sitewide times are in their local timezone. I've managed to do that, but my question is, what about daylight savings time? Is there a way to calculate it automatically, via php, or will I have to resort to asking my users to input their dst offset manually (those poor things), or should I not even bother with it? Thanks in advance.