try this, I have no idea if it will work
Copy all the files from the FW HD to your mac, then use Disk Utility in OSX to format the FW HD in DOS FAT format, now check to see if windows will recognize it, then see if the mac will recognize it, then move all the files from the mac back to the FW HD and everything should go fine
This works because Windows has a slight problem reading Mac formatted discs, but Apple says OSX can read FAT partitions, if this is true, what I described above should work. But I don't think OS9 will be able to read the FW HD without third party software, but that is the best solution I can think of.