Shortly after I posted I started thinking about swapping drives in the PB... then I realized...Duh!?!... the 640GB drive was SATA!... anyway the only 2.5" IDE drive that I had on the shelf was known to be somewhat 'squirrely'... gave it a shot... popped it into a portable firewire box and installed 'Unsupported OS9' the same way. Seemed to go easier this time, however at clicking 'OK' at the 'Installation successful' message, I got a system bomb!
Plugged the Firewire drive into the PB and "option" started with the OS9 firewire and it worked again, booting the PB into OS9. Weird thing was that I had no 'top row' menus ... just the 'OS9 Lives' icon, the OS X drive icon and the trash bucket! Changed the screen resolution and restarted, after which I had all the menus back.
Dismantled the PB and installed the OS9 drive but only got the 'blinking ?'... took it back apart and reseated everything but got the same result.
Wound up putting the OS X drive back in the PB just to make sure that it still worked and that fired right up.
Sooo... I'm thinking I need to try again with a fresh drive. I'll put the 'flakey' OS 9 drive back into the firewire box and see if it still boots the PB.