The Internal ATA bus only supports 128 gig, if you install a larger drive it will only see up to that limit
If you need a bigger drive you can do 2 things
Install a mac compatible ATA or SATA pci card (expensive)
Install a cheap USB2 card and attach an external USB 2 drive (the USB 2 card will not have the size limit, I know, I have a 500 gig drive connected to my G4)
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