Hi I have a 867Mhz TiBook. The last models were 867Mhz and 1Ghz. They will run Leopard. I do, with no special tweaks, hacks or installers. And it runs it lovely. --- I'm afraid if you have a Ti Powerbook with only a G4 processor, you won't be able to run Leopard, which, I believe is 10.5, the highest you can run is 10.4.11