Drupal's timezone configuration does not seem to be automatic, at least in Drupal 5.0. Each time a DST configuration changes you need to do the following:

• Log in as an administrator in the navigatino block
• Go to Administer -> Date and Time
• Set the timezone in the Default Timezone selection list. The timezone is either GMT -600 or GMT -500. Usually in the winter time (Nov -> Apr) timezone should be GMT -600. In the summertime (Apr -> Nov) it should be GMT -500.

It would be very good to have this be automated, which will occur with the next upgrade to Drupal.