There aren't too many options when it comes to data recovery on Apple based computers. Whether you have a Powerbook or an iBook when things go wrong, they really go wrong. No amount of fiddling will get your OS back to how it was. Software just as Time Machine put the emphasis on backing up your data. If you manage to find any software it may be wise consult a professional before making things worse. The Apple file system is very finicky. If data recovery costs exceed your budget then try the DIY options.