Microsoft Knowledge Base Article 914837 contains the following summary and introduction:
SUMMARYOn April 2, 2006, Indiana will start using daylight saving time. Most counties in Indiana will use the Eastern Time zone. However, some counties will use the Central Time zone.
Microsoft Windows users in Indiana will have to change their Windows time zone settings from Indiana (East) to either Eastern Time (US & Canada) or Central Time (US & Canada). The Indiana (East) time zone setting will become obsolete and should not be used in the future. Indiana residents should use local sources of information to determine the correct time zone.
This article describes issues that are related to the time zone changes in Indiana. This article also describes how and when to change the time zone setting. How you make this change depends on whether you must change one computer or many computers.
INTRODUCTIONOn April 2, 2006, all counties in Indiana will start using daylight saving time. Residents who are in the Eastern Time zone will set clocks forward one hour on that day to start using Eastern Time. Residents who are in the Central Time zone will not change their clocks on April 2, 2006, but will start using Central Time.
Currently, Microsoft Windows products contain the (GMT -5:00) Indiana (East) time zone setting. This setting does not use daylight saving time. You must update Windows-based computers in the affected time zones as follows:
Eastern Time zone
If you are in a county that will use the Eastern Time zone, set your time zone to Eastern Time (US & Canada) as soon as possible. If you do this, new meetings or appointments that repeat and that you set up between now and April 2, 2006, will be accurate.
Central Time zone (before April 2)
If you are in a county that will use the Central Time zone, we recommend that you do not change your time zone until April 2, 2006. This step helps prevent the wrong offset for meeting requests between now and April 2.
Central Time zone (on April 2)
On April 2, your actual time will not change, but you will officially move to the Central Time zone. Your actual time will change in October 2006. However, you must change your time zone on April 2 to Central Time (US & Canada), and then reset your clock to the correct time. After this change, you may have to update or resend requests for meetings that repeat and then verify other meeting requests in your calendar programs. This step will enable the computer clock to automatically adjust in October. Therefore, any new recurring meetings that are created between April 2 and October 28, 2006, and that are scheduled for a date on or after October 28, 2006, will be correct in your calendar.
Important You should not wait until October to adjust your clock.
Note You should use local information to determine which counties will use Central Time and which counties will use Eastern Time.