Upgrading an old iBook G4 to MacOSX Leopard (10.5.6)

A friend of mine bought a used iBook G4 on ebay and asked me if I could "upgrade" it to 10.5.6. I thought this can't be that complicated and said yes, which turned out to be a bad decision after all. He gave me a disk image file of the MacOS X 10.5.6 Install DVD (6.2GB in size) and the first thing I wanted to do is to burn this dmg onto a dual layer DVD+R recordable. Of course, I did not have such a medium at home and after all, they're not really cheap (~€4 for a good quality disc). Burning dmg files directly onto discs is no possible on Windows as it seems and I don't think that k3b allows for burning dual-layer discs currently, well, I haven't really tried though, so if anyone can confirm that this would have worked, please tell me.
I tried several tools to convert the dmg file to a format which is writable with Nero or any other burning tool on windows, like dmg2iso, dmg2img (the successor of dmg2iso), MagicISO, PowerISO, ... None of them worked. dmg2i* complained about a corrupt plist in the dmg file, MagicISO said that the file is damaged and can't be read or cannot be found (that's an oxymoron, if you ask me, how does the tool know that the files is damaged if one of the possible error causes is that it cannot find the file?), PowerISO said quite the same.
I then wanted to verify the dmg file by trying to mount it with MacDrive, which worked out of the box and I could access all the files in the disk image.

I then booted the old Mac, copied the dmg over there and verified that it really works. I then played a bit with "hdiutil" just to find out that it actually is able to convert the dmg to a CD/DVD Master image (.cdr) with the following command:

hdiutil convert /path/to/filename.dmg -format UDTO -o /path/to/savefile.cdr

After I did that, I had an about 6.2GB .cdr file which I then in turn copied back to my windows machine to burn it there to the DVD DL medium (the iBook G4 did not have a DVD writer, that's why).
After burning the disc I verified with MacDrive that the disc is accessible and plugged it into the iBook then. To my surprise, nothing happened. Well, nothing is not correct, it just spat the disc out again as if it would be unable to read it. I know that the drive in the iBook is capable of reading DVD DLs because my friend burned the dmg file onto the disc and tried to boot off of it (which of course didn't work ).
I then tried to tune the settings of my burning tool, created another .cdr file now with Disk Utility instead of hdiutil which resulted in a 7.2GB .cdr file (the dmg was compressed, mhm) but nevertheless, this image also didn't work on the iBook after I burnt it onto the disc.
After having wasted 4 DL discs, I restored the dmg file on the Mac onto my brand new 16GB usb flash disk and tried to boot from it, which didn't work as the firmware of this specific iBook model doesn't seem to support booting from USB devices (firewire would have been possible, but hey, who has firewire??).

OK, as a last resort, I wanted to somehow install the new version from the harddisk, meaning that I'd have to re-partition it but of course, there was just one partition on the 30GB disk and this partition held the system partition and was not resizable. Duh.

OK, reinstalling with the old MacOSX version (10.3, I think), changing the partition layout to have a spare 8GB partition after the system partition and after the installation has finished, I restored the dmg to this partition and from that point on, everything went smoothly.
After the installation has finished, I removed the second partition again and resized the volume on the first one to extend to the maximum physical space and everything was good again.

Time wasted: ~15hrs
Time worth: ~1500€
Revenue gained: 1 DL disc and a breakfast
Perception: Next time, say no.