Trying to keep my little post alive, hoping to hear from someone with some insight...
I noticed this about the 10.3.8 update:
"Addresses an issue in which a PowerBook G4 computer would, on rare occasion, wake from sleep with a black screen and not respond to any keyboard, mouse, or trackpad input."
Ah ha!!! related--yes, the same problem, maybe not.
(last time I beg, I promise)