The protocol for Sharepoint is documented; see http://msdn.microsoft.com/library/default.asp?url=/library/en-us/spptsdk/html/tsstsync.asp

A sample application is at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odc_ol2003_ta/html/odc_OLOutlookCalendar.asp