This is the spec of my nephew's iBook:

Hardware Overview:

Machine Model: iBook G4

CPU Type: PowerPC G4 (3.3)

Number Of CPUs: 1

CPU Speed: 1 GHz

L2 Cache (per CPU): 256 KB

Memory: 384 MB

Bus Speed: 133 MHz

Boot ROM Version: 4.7.7f0

Serial Number: UV3441SQPH0

Firmware is up to date too.

I now think it is a Machine Specific Disc problem as it won't install a package either.