Digital library interoperability for both documents and metadata is a critical and complex issue. Although many relevant standards have been developed, and continue to evolve, in practice things are not quite so easy as they seem. We have built a software environment called the Exchange Center that helps digital librarians manage the process of sourcing documents and metadata from various repositories, adding local content where necessary, and exporting the resulting collection into formats that are suitable for digital library repositories. This paper describes the software, which is built on Greenstone but does not require its use as the final digital library server.