I'm having this issue right now. I have an iMac G4 with the nvidia card if that matters at all. When I boot from the cd I made from that .iso it pretty does nothing and than says "rebooting in 180 seconds".
It's a bummer I was hoping to get this ancient machine up and running with something that could support a modern browser (for facebooking or whatever).
Well, if all you need is something that can support a modern browser, PPC Macs running Mac OS X v10.4 Tiger and 10.5 Leopard can use TenFourFox