Currently Being ModeratedFeb 20, 2013 1:52 AM (in response to gestebis)
The highest your PowerBook can go to is Mac OS X 10.5.8 Leopard.
Anything beyond Mac OS X 10.5 requires an Intel processor, which the PowerBook doesn't have.
You can obtain retail copies of Mac OS X 10.5 Leopard online from sites like eBay or Amazon, some online Mac software vendors may still have copies.
Be warned, the software is not cheap to buy.
Best of Luck
Currently Being ModeratedFeb 20, 2013 5:52 AM (in response to gestebis)
As knucklesmac has said this is possible. However, something that might work is trying local MUGs near you (Mac User Groups) to source install discs. My local MUG allowed me to source OS X 10.1 install discs for just £2.50!
Currently Being ModeratedFeb 20, 2013 10:24 PM (in response to gestebis)
Do you need Leopard? What version PowerBook G4 do you have?
Currently Being ModeratedFeb 23, 2013 6:54 AM (in response to gestebis)
Mac OS X 10.5 Leopard installation system requirements
Look on eBay or Google the installer part numbers to possibly find at an on-line store. Here's what to look for:
MB427Z/A Leopard 10.5.1 install DVD
MB576Z/A Leopard 10.5.4 install DVD
MB021Z/A Leopard 10.5.6 install DVD (single user)
MB022Z/A Leopard 10.5.6 install DVD (5-user family pack)
Installing Mac OS X 10.5 Leopard
Mac OS X 10.5 Leopard Installation and Setup Guide
After you install the base 10.5, download & install the 10.5.8 combo update at http://support.apple.com/downloads/Mac_OS_X_10_5_8_Combo_Update
The DVD should look like this
Caution - Leopard does not support classic mode. So, if you currently open OS 9 apps in classic mode, you won't be able to do this if you upgrade to Leopard.