I received a request to install iTunes 10 on a G4 Powerbook so they could sync their iPhone 4s. I found that their version of OS X would not support iTunes 10 and they need to upgrade to OS X 10.5.8 which is the highest release that still supports PPC processors from what I could find. They also need a new battery and very likely a new PRAM battery as well.
So what I am going to do is :
Doing a full backup of all data before upgrade
adding 1GB of ram (allowing them to max out at 2GB)