Even though I had been keeping up with the (infrequent) firmware updates for the Z3100, in doing a new upgrade to the HP-APS software I received a message that my firmware was not the current version. Hope alive again, I went to the HP website for my printer and Windows 7, but there was no listing for firmware for it. I then re-downloaded the Vista 64-bit firmware and it successfully installed on my printer. Oddly, the LCD on the printer listed the same firmware number it had before! TR12PS_18.104.22.168, PS 3017.102-02.95R, OS TR-2.0.11.
However, upon the printer's rebooting, the Color Center swept into action, with the message "Completing the synchronization of paper presets" or something to that effect. Now, opening the printer driver I found all of my old custom papers!