Do you have backups? If not, stop trying to use the laptop or you may end up with the hard drive dead completely which will mean either 0 data or lots of £££ to get it back.
Three solutions:
1. Buy a MacBook/Pro laptop and a Firewire cable. Boot the PowerBook into Target Disk Mode, hope it mounts and hope that you can recover your data from it.
2. Replace the drive in the PowerBook, put the old drive in an external enclosure and hook it up. Then hope that you can recover data etc.
3. Wait until you go home, hook the PowerBook up to another Mac using Target Disk Mode and a Firewire cable (assuming you have another Mac) and then see if you can recover data.
If you do have backups, then the solutions are the same, minus trying to recover data but instead just restoring it from backup.