Problem Upgrading G4 MAC to OS X

A client brought in a G4 MAC with a CD ROM, 384 MB RAM and a 10 GB HDD running OS 9. She wants to upgrade to OS X and produced several DVDs which she said were the OS X system discs from her iBook. I attached an external DVD Writer and set the system startup to boot from it but it will not boot from the DVD. Get a folder with alternating question mark and happy face instead. Is this because the G4 cannot inherently boot from the DVD or are the DVDs specific to the iBook? Or ….? I’m wondering if it would be practical for her to purchase a fresh copy of the OS X – which still might not boot the G4. Some input from my colleagues out there would be appreciated.