My powerbook is running almost four years strong! With this one you're considering, if I were you I would just make sure that it won't have the screen defect that was plaugeing some older PBs. http://www.acmetech.com/extras/apple_powerbook_g4_recall.htmlI think you're good to go, though.
Also, I would bump up your memory to >1GB to smooth leopard performance, and I'd also replace the hard drive just to avoid frustration later.