@ muffie - Which model of PowerBook G4 is it? A1106, A1138, A1046 or something else, i.e. A1095, etc.?

As it seems to look like a 15.2" model.

If you're not bothered about which model you have/use, as long as it has 64MB then it still should be fairly easy to get hold of a replacement PowerBook, and transfer the licence to that replacement system. In which case you'd probably only need to swap over the HDD, you'd then still be able to utilise the power supply for your current PowerBook, as well as any battery you might have been using up until now, etc..

Getting hold of a 64MB MacMini will probably be more difficult, though I don't know what they go for currently, but probably a PowerBook would be a cheaper, more available option.

I don't know which country you're in, but if getting it apart would be too much for you, if you live in the UK then I'd help you get whatever's salvageable from inside your system, saved for your replacement system.