Hi Steve A couple of issues with putting a new HD in a G4: 1) The internal workings of a G4 (addressing limitations) will only recognize 128GB of disc space. So if you install a 250GB HD you will only have 128GB of useable storage. If the same drive were to be used externally, in say a Firewire enclosure, the machine would see the full capacity. 2) I have had endless problems getting 2 drives to work on the internal IDE buss, especially if the drives are from different manufacturers. One has to experiment with jumper settings, the obvious just doesn't seem to work sometimes!!? Good Luck John