Okay so OS X Leopard is the OS 9 killer.
Does anyone know of a work-around to install OS 9. I have the latest iMac with Leopard pre-installed. I tried partitioning the hard drive and then uploading OS 9, didn't work. I guess it would have to be something that overrides the firmware, if that's possible.
In case you are asking why, it's because I have a scanner and a printer which are not made/imported any more, they work perfectly but no OS X Leopard drivers are available, or ever will be.
This is a bit complex, but the short answer is, no. The intel based iMacs can't natively run OS9 because it was written for the IBM powerpc processors. It was working in 10.4(tiger) because Tiger had emulation software to run it. Apple took the emulation software out of it for Leopard. There are commercial applications to allow you to run classic in leopard, but you cannot boot to it, and the drivers will not load anyway. Hope this helps.
P.S. apple no longer uses an open firmware interface, instead they now use Intel's EFI interface. A mac nowadays is just a really pretty PC, so you'd have about the same chance of success installing OS9 on your winblows machine.
I do have a HP scanner that does not have drivers for OSX (and probably Vista as well).
I made it work with OSX via SANE. You'll need to read a bit to discover what device your scanner maps to (mine mapped to a specific chip, just like an "IBM ThinkPad Wireless NIC" will map to an Atheros hardware).
After that, and some trying, I found that I could only scan using "Browse Devices" inside Image Capture.
But it worked nicely, and SANE is the culprit I have not upgraded my HP 2200c scanner :-)
If you have a PowerPC based Mac, like a G5 or a G4, you can borrow the Kernel and Classic related software from a 10.4 and earlier installation. The kernel is the limiting factor in Classic compatibility in Leopard, 10.5.
As stated above, you can make use of SheepShaver which will run most, but not all Classic software. Make sure you use the latest builds from the www.emaculation.com/ web site. With SheepShaver you can install up to 9.0.4. Another option: you can use Basilisk II which will install up to Mac OS 8.1.
For either SheepShaver or Basilisk II, you must have a boot-ROM from specific Macintosh computers. Again check the forums on emaculation.com
I have been running both on a Power PC G4 Tower unit for the past several years. However, I don't remember what I had to do for this, but I don't recall that it was difficult. I still have some old programs that I use that require the Classic operating system.