We have several macs - most of them run under OS9 with only 3 under OSX with DVD writers. Do not understand why the OS9 macs cannot read the OSX DVDs.
George,
Those OS 9 model Macs may not have a DVD drive but only a CD drive which means it will only read CDs.
To check, Go to the Apple menu on one of those OS 9 Macs and select Apple System Profiler. When it comes up, click on Hardware. After just a few moments it will show you the drives attached to the computer. It will state whether you have a CD drive or a CD/DVD drive.
It they do have a DVD drive, then you could be missing the Apple DVD Player.
Depending on the model of those Macs will depend on which version to install.
Macintosh G3 and G4 computers shipped with AGP graphics display cards.
http://docs.info.apple.com/article.html?artnum=120022
PowerBook G4 systems with 550 MHz or 667 MHz G4 Processor
http://docs.info.apple.com/article.html?artnum=120105
If you already have iDVD installed on these computers, you probably need to install the update.
http://docs.info.apple.com/article.html?artnum=120045
You should also be running OS 9.2.1 on these Macs.
http://docs.info.apple.com/article.html?artnum=75288
Do not install OS 9.2.2 unless you plan on installing OS X on those machines.
Let me know if this helps you.
Cheryl