Windows 2003 SBS and Exchange

Hello, I recently came across a client who has 10 users connected to a WIndows 2003 Small Business Server with a domain. The server is the dhcp and dc for the network. The funny thing is that this system was setup without exchange being installed. The client wants to put exchange on the server. I’m concerned since the system was in initially setup with exchange, I’m worried about the active directory becomming corrumpted or something worse. Has anyone installed the Exchange option on a SBS server after primary installation of the O/S?

Thanks,