OK. My powerbook is the February 2000 model. The one with firewire. I did have Mac os 9 on 10gb of the 18gb and then an 8gb partion for mac os x. I installed the firmware update, and when it rebooted after it was installed, it was the mac version of the "Blue Screen of Death". Yes, its the sad mac icon at startup. i also have 512mb of ram, no airport card either. If u need anything else, email me at firstname.lastname@example.org
Just a suggestion:
Check if you have the correct ROMUpdtFile.
Remove all optional RAM.
Reboot the machine with CD.
Set startdevice CD.
Start with CD.
Use a second mac with ethernet to make the ROM upgrade again.
Or: Connect the 'Book as an external FireWire drive to another Mac (Target-Mode, start with "T" pressed).