I'm not sure who this helps, but I just wanted to share how I was able to
use the iMac G4 15" (USB 2.0, Late 2003) Restore DVD, which I burned to a
DVD, and which was not entirely readable by the iMac's finiky Combo Drive.

While I was able to use the disc to restore the stock MacOS X 10.2.7 system
software, with all the options, the disc was having difficulty running the
system restore phase of the install (after MacOS X is installed). Like a
poorly burnt DVD, or slightly-incorrect DVD-R format. My burner, on another
computer, could only burn at a minimum 8x. I'm blaming this for the poor DVD
reading.

Anyway... here's how I was able to finally get the Restore completed.

As you know, there are two parts to the System Restore -- installing the
System Restore App, and then running it. After the first part is done, the
System Restore requests that you put in the DVD again. It won't budge for
anything but an actual, physical DVD that matches what it's looking for.
However, as above, that DVD doesn't read the restore parts too well.

What I was able to do, however, was:
1. Mount the Disc Image of the Software Restore (the Toast or ISO file
backup of this DVD)
2. Run the System Restore
3. It will request you insert the DVD (even though an image of the DVD is
mounted)
4. Insert the DVD as it asks. It'll verify, and present options for
restoration

HERE'S THE TRICK...
5. Rename the /Volumes/iMac System Restore 1 folder (the DVD mount point,
having the '1' because it is the same name as the already-mounted ISO) to
/Volumes/iMac System Restore 2
6. rename the /Volumes/iMac System Restore folder to /Volumes/iMac System
Restore 1 (the previous name of the DVD mount point)
7. Select any/all of the System Restore options, and away you go! All
options you select will be successfully installed (provided your image, or
hard drive, is not currupt).

You'll need to reverse the naming, OR restart your computer, in order to
Eject the volumes.

I'm not sure who this helps. I'm also not sure if there was an easier way to
do it, but this finally enabled me to install the System Restore bits to the
iMac G4 15" USB2.0 with a finiky Combo Drive.

--
James from Canada