Hello David,
Did you also install the Compenius sample set? It sounds like you overlooked that. Oberwerk itself is a separate installer than the included samples so you need to also install the included sample set. Please insert the Oberwerk DVD, then in Hauptwerk go to File | Install organ, temperament... navigate to the DVD drive where your Oberwerk DVD is then choose the Compenius installation files. You need to install each of these files through the Hauptwerk component installer.
Once installed, after you create the ODF in Oberwerk and then save it to the proper location (OrganDefinitions folder in the Hauptwerk directory) it will load the specified samples from the installed Compenius sample set.
Please let me know if that helps.