A cry for help!!

Having taken it home to fix the Powerbook boots but then asks for a password to to log on. Nobody knows what the password is. I have tried booting from an OSX disk but the CD/DVD drive is broken and it will not boot from this so I cannot reset the password this way.
It will boot into target mode and I can mount it as an external firewire drive on my iMac or Macbook.
Any ideas how I can fix this Powerbook as its too good to bin. I don't need to recover anything off it just reinstall the OS.
Any help or advice would be greatly appreciated.
Paul