Mail store when server joined to Active Directory

Planning on replacing Open Directory with Active Directory.

Our Open Diretory Master is also our mail server.

If I change to to "Connect to server" and set it to authenticate against Active Directory, it will destroy all the Open Directory users. These users have duplicate accounts in Active Directory. How do I get the mail stores associated with the new AD accounts instead of the Open Directory accounts or somehow migrate the date to the new accounts?

The short names would stay the same so could tie it to that if somehow possible.

I have the same question for iCal and iChat data.