Ran into an issue where I could not reset the sync data on my 10.6 Mac. After pouring through a number of help documents, I came across one that worked. I am linking to it and two additional ones I found helpful.
1) Mac OS X v10.5, v10.6: Resetting the SyncServices folder – http://support.apple.com/kb/TS1627?viewlocale=en_US
2) Sync Services: Advanced troubleshooting for contact and calendar syncing – http://support.apple.com/kb/TS2481
3) MobileMe: How to reset sync data – http://support.apple.com/kb/HT1497
While the link below is not an Apple Support document, it did lead me to the answer.
4) How to Manually Delete all Sync Data from MobileMe’s Servers – http://robulack.wordpress.com/2009/04/01/how-to-manually-delete-all-sync-data-from-mobilemes-servers/