Many companies have custom scheduling, time calculation or billing applications that are date dependent. Calendars, both business and personal are also impacted by this change. The change also impact international companies as well, particularly if they interact with servers in North America.
Under the new law, Daylight Saving Time (DST) will start (spring ahead) on the second Sunday in March and end (fall back) on the first Sunday in November.
Microsoft has provided considerable information on update availability in Preparing for daylight saving time changes in 2007, including links to updates for supported operating systems and servers. Note also the following information which will be helpful for people who have not yet replaced an operating system that is beyond the "life support" by Microsoft:
All versions of Windows can be manually updated using the tzedit.exe utility or other techniques documented in Knowledge Base article 914387 and similar articles for other countries, which is the preferred method of remediation for any product outside of Mainstream Support.