I format the 2GB SD card in the camera using Low-Level format.
Move it to USB reader on Mac.
From malbe.nm.ru/chdk/ download allbest-a650-100d-34.zip
Use unzip in terminal window to unzip -- produces only a DISKBOOT.BIN file, no PS.* file.
Copy DISKBOOT.BIN to card, put in camera -- no menu item
On the mac, execute touch PS.FI2
Back in camera, now have menu item but it produces "Update File Error!!!"
Try again with DISKBOOT from allbest-a650-100d-16.zip (mentioned in another forum message)
This package contains PS.FIR file, which I copy to the SD card and rename PS.FI2
Still get the Update File Error!!!"

What am I doing wrong?
(p. s. checking with the OS X Disk Utility, it says that the SD card is formatted MS DOS FAT 16.)