If the cd came with his G4, it might have different drivers in it for the hard ware in the older iBook. Try it, you wont run into any problems such as activation or serials like Microsoft has. Worst case scenario it doesnt work and you call apple or go to a store tell them you lost the cd's , bring a proof of purchase and they should be able to help you out. I don't think they will give you panther though, they will most likely give you whatever came with the G3 at the time, perhaps Jaguar?