Your questions: "Just what is rebasing in daylight saving time?"
In order to be prepared for the DST 2007 changes, we recommend that customers install the Windows OS update for DST (KB 931836, also available via Microsoft Update if you don't want to wait for it to install via Automatic Updates). When you install this update, appointments on your Office Outlook calendar that occur during three weeks in March and one week at the end of October and beginning of November to be off by one hour.
To address this issue, you then use the download and run the Outlook Time Zone Update Tool to update your Microsoft Outlook calendar items that fall in the extended DST period in 2007. The Outlook tool updates the Outlook appointments that were scheduled prior to applying the DST 2007 Windows OS update. The Outlook tool is referred to as rebasing tools and allows users (or IT administrators via the Exchange wrapper) to adjust – or ‘rebase’ – these appointments.
Microsoft Office Outlook 2007, the newest version of Outlook, can automatically update a person's calendar to conform to the new daylight saving time rules. However, the Time Zone Data Update Tool contains additional improvements that are not available in Office Outlook 2007.