Right after posting Beta3 I downloaded it and verified everything worked as specified in the user guide.
Beta3 changed the layout of the distribution to be consistent with jBPM jPDL 3.2 (currently in beta status as well). Our new organization makes a difference between the development and the distribution layouts, for production reasons.
I guess the build files you refer to are the scripts to rebuild the libraries. These are effectively missing from the distribution. If you want to work with them you might want to check out the project from CVS instead. Alternatively, I could provide a script to rebuild jbpm-bpel.jar from the sources in the distribution. Let me know how you want to proceed.