This update, which is published as Microsoft KB Article 951072 supersedes and replaces the December 2007 DST Update (Microsoft KB Article 942763). This update also includes additional time zone changes that were signed into law after the update in Microsoft KB Article 933360 (August 2007 Cumulative DST update for Windows) was released.
If you have already deployed the December 2007 DST Update, please review the information in Microsoft KB Article 951072 to determine whether you need to deploy this update immediately. For Exchange specific DST information, please refer to the Daylight Saving Time Help and Support Center and as well as the Exchange team blog.
More info: Daylight Saving Time Help and Support Center