I'm making some progress. I enabled User Access Control, checked the Run as Administrator box, and reinstalled PMM 3.92. This time the program paused during install and I was able to insert the hacked ATT voices file during the install and the installation completed successfully. However, now the PMM does not recognize my DMS, giving me the message "error retrieving DMS drive ID", telling me to close Nortion, Media Player and Notepad. Any thoughts about this would be appreciated.
(As an aside I installed a Virtual machine using VMware 6.0 and installed XP and PMM 1.86 on the virtual machine. I can now run XP from within Vista and am able to add new songs, playlists and voice prompts on the DMS. Not an elegant solution but at least it works.... though I get a different voice.)