I'm maintaining a mapping data between the IANA tzids and Windows time zones in the Unicode CLDR project and review the data about quarterly basis [http://www.unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml].
It looks Windows 8.1 start providing an API returning an IANA Time Zone Database ID [http://msdn.microsoft.com/en-us/library/windows/apps/windows.globalization.calendar.gettimezone.aspx], but I did not try it yet.