Yes, you can install 10.4. Even the earliest 15 inch G4 PB can go up to 10.5.8. How much RAM does it have? You need a bare minimum of 512 MB and 1 GB would be preferable. Does the hard drive have enough space for the installation? 10.4 will take up about 4 GB and you should maintain free space of at least 5 GB (and preferably 10).