I don't have an answer for you but I have a similar problem. I synch with my Axim and my wife synchs with her Jornada. We don't use separate WinXP logons so are synching with the same Outlook files. I've set my Activesync calendar settings to only synch with events in my category and for hers to synch only with items in her category. My desire is to allow each of us to delete the other's calendar events on the PPC without having the deletions trickle through to the others PPC. Unfortunately, that doesn't work. Either Activesync or Outlook seems to ignore the categories.
