This happened to me a while back with a FW HD. I still occasionally have problems with other FW drives, but not as severe. You could try these options to recover the data:
1. If you have access to a desktop machine, try removing the drive from its enclosure and mounting it internally as an IDE drive.
2. Unplug the FW cable. Reboot your PowerBook, wait until the startup process is complete, then turn on the power to the FW drive. Then plug in the FW cable. Repeat this process a few times until you get the drive to mount.
3. You can also try <a href="http://www.alsoft.com" target="_blank">Disk Warrior</a> to rebuild the directory (if you can get the drive to mount after booting from the CD).
Good luck.