If you get (as I did) when trying to play certain DVD movies in PowerDVD XP 4 the following error message then you'll have to get and install the patch listed below.
title bar: DVD Error
error code: 89030000
Unknown file format
patch can be found here: http://www.cyberlink.com/multi/download/dl_patch_82_1_ENU.html
This error message occurred on a Windows XP SP2 box. Not sure if it happens on other platforms, who knows?