Thank you for your reply,
I found the answer, multiple organizations are not supported because of Exchange 2003 integration with Windows 2003 Active Directory. There is only one Exchange organization allowed per Active Directory forest. During setup, there is no option to create a new organization for the second Microsoft Exchange 2003 Server computer installed into a Microsoft Windows 2003 forest. It can only join the existing organization that was configured during the installation of the first Exchange 2003 Server computer.
Regards
CF