you can't make it change to DST without having some way of knowing when that timezone changes to DST - http://timeanddate.com/time/dst2005a.html you can obviouly do it on when the server changes to DST but that might not be when other people change if they change at all.
edit: infact punbb probably is affected by the DST on the server atm since it uses date and date is affected by DST since is just uses the current time on the server, question is... is another way better?
Daylight Saving Time begins for most of the United States at 2 a.m. on the first Sunday of April. Time reverts to standard time at 2 a.m. on the last Sunday of October. In the U.S., each time zone switches at a different time.
In the European Union, Summer Time begins and ends at 1 am Universal Time (Greenwich Mean Time). It starts the last Sunday in March, and ends the last Sunday in October. In the EU, all time zones change at the same moment.
the EU (its the the european law that they all have to be the same) and the US are easy
then you get
Start: the first day of Farvardin
End: the first day of Mehr
which is guess is a lunar calendar, and since its not even whole timezones that change its per country... i don't see how its possible to get all the times perfect