I do not have a Treo, so I am not sure how it works, but
Airset offers syncing and sharing. This is from the Airset site "With the AirSet Desktop Sync client, you can synchronize Personal contacts and calendar data for one or more groups between AirSet and Microsoft Outlook, Pocket PC devices, Palm Desktop, and Palm Devices. Currently, the sync client only runs on Microsoft Windows PCs. "
I have used Airset in the past and it is a great tool and best of all it is free. I hope it works for you.