Newb trying to setup Mac

Hi guys, hope you can give me some pointers.
I have a G4 Powermac, and I'm trying to update the OS.
A mate has given me a DMG file of the os, if I double click it will mount it on the desktop.
If i then click the install icon it says it will reboot and then install after reboot, but it just reboots and then sits there as if nothing has happened.
The original DVD drive doen't work, so I put my Pioneer 112 in it. This is recognised as a DVD-ROM only so I can't burn the image from the Mac to DVD.
I Have tried copying the file to a USB stick and booting off that but when I go into the boot menu (holding option) it only lists the HD as a bootabel device.
I have tried using Nero on my pc to burn the image to DVD, by renaming it as an ISO. The files seem to be there but some of them have lost their associated icons.

I've lived with PC's for years but never really played with Macs before so I've used up all my ideas.
Help!
Cheers!

try downloading the latest image 10.6.3 in the usual places. do u know what version you powermac will take?

Out of curiosity, what OS are you trying to install? I think the latest (Snow Leopard) isn't compatible on PPC, Intel only. (Unsure about Leopard, I know for sure Tiger works on a G4 as I had it on my Mini)

I created my OSX SL DVD with UltraISO... pop into the Mac and boot whilst holding C and job done.

BTW - I thought booting whilst holding option should still list the optical drive even though there isn't any media there... could be wrong though.

^^completely correct but leopard should also work work on PPC.

10.6 is intel only afaik.

your g4 will need a disc of 10.4 or 10.5 depending on how old it is

It was 10.4 that I was trying. Will try 10.5