Mac OS X 10.5 Leopard was the last operating system to support the PPC Macintosh computers. 10.6 Snow Leopard dropped its support for PPC.
What you can do, if possible, is to instal Ubuntu (which is linux) on your Power Mac G5 and hopefully there are drivers that support your hardware. I never done it before, but i was thinking about it when i wanted to continue using my 1.2 GHz iBook G4. Instead i just gave it to my dad.