Exchange 2003

I had some issues when I first installed Exchange 2003 as it was installed on a DC when I had intended to install on a seperate server as a mail server only.
I have moved over the mailboxes etc, and want to delete exchange from the DC and have exchange on the second server only.
I am getting an error about mailboxes stil not moved or deleted that is preventing me from deleting Exchange 2003 on the DC.
As far as I have checked I have removed all the boxes. Any idea how to proceed from here?
The client intends to host exchange on the second server.