I have 2 orig. ibooks and also found out that 10.4 (retail) wouldn't install on them. Yes because they don't have a firewire port. I have read however, that the can run 10.4. My only thought is to take out that 3 GB HD and install a larger one, as you'll need it for an OS of that size. You might want to try to install on the new larger HD while it is NOT in the ibook. If you have an external firewire drive you wouldnt mind opening up. You could put a HD in it, install 10.4 on it, remove it from the external device, and now physically install the 10.4 loaded HD in the ibook G3. Not sure if that will work but would get you around the no firewire thing. I saw this as too much of a hassle and am running 10.3.9 on both g3 ibooks.