i have a powerbook g4 that has os x 10.5.8, when i try to do software updates it says there are no updates how do i fix this?

There are no further Mac OS X updates or upgrades for that configuration. Click here if you're running an iTunes version prior to 10.6.3.

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It is impossible to install any Mac OS X version newer than 10.5.8 on it.

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For clarity, all operating systems after OS X 10.5 Leopard require an Intel processor. Your Powerbook has a PowerPC G4 processor.