Alaric, I have the same model of G4. These machines will not recognize hard drives beyond 128gb. This is due to limitations in the firmware. However there are two ways around this. The first is to buy an added ATA card. They are quite expensive for Macs but this way will also allow you to add more hard drives as they give you extra controller capabilities. The second method is what I went with and it is a small program called ATA Hi-Cap Installer. I went with this approach and it was simple to install and it works very well. I installed a 160mb drive and I can access 152.67mbs of it. http://www.speedtools.com/ATA6.shtml It should cost around 19 or 20 Euros. The Intech web page explains it all quite well. Bill Montreal