I have an ibook g4. Did not boot anymore with a broken folder at the startup. Disk utility could not fix, so I shelled out $100 to get Diskworrior and fixed this problem. I was able to get back on and save the files. After few days, same problem again. Does that mean problems with hdd or other hardware?
Replacing hdd seems rather complex tasks. I did not do a clean install (tiger) after the first crash. Would that have helped? What should I do after diskworrior save?

When you boot from yoru installation CD/DVD and run Disk Warrior, check the SMART status. If it says "Verified" it's unlikely that your HD is failing. It is possible that you just need to reinstall the OS.