The official minimum install for 10.5 is 867 MHz; so your model *JUST* missed it. Although 10.5 generally can be made to install without issue on systems that are just under that spec. I have a G4 Digital Audio, one generation older than the minimum-supported for 10.5, and it installed just fine even with a 450 MHz CPU, using an OpenFirmware trick. It ran just fine when I upgraded to a dual 1.0 GHz, and then to a single 1.5 GHz. It also runs fine on my minimum-spec PowerBook G4 867 MHz.