The Mac OS X 10.5 Leopard cannot run Classic Mac OS 9, but Tiger 10.4.11 could; it was the last OS X system to allow use of a non-boot Mac OS 9 system under OS X. Leopard cannot do it.
So you may have to look for an older PowerPC G4 or G5 computer with Tiger OS X 10.4.11 and the Classic OS 9 software; or an even older PowerPC G3/G4 with Mac OS 9.2.1 installed to run vintage obsolete software.
A second system, if supported, of Tiger 10.4.11 on externally enclosed hard disk drive with a firewire connection could run a computer; an external enclosure should have an oxford-type chipset to facilitate booting Mac OS.
If the iMac G5 (20-inch) shipped with a Tiger install-restore disc set, you may be able to use that to install a complete system; the second grey disc included with such an install set may include Classic OS 9 installers. Rather than revert the iMac to the older OS X so as to run Tiger and Classic, this is where an externally enclosed FW hard disk drive comes in.
OWC macsales has some that are fair examples of a good idea.
http://eshop.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB
The older port style w/ FW400 & USB2.0 is my choice to boot Mac system/clones w/ FW
http://eshop.macsales.com/search/Elite+Pro+Oxford+934
It should have a power supply and 7200RPM HDD, an oxford chipset, etc. They have these in aluminum cases; with or without a hard drive installed. And every once in awhile, I look through there.
Good luck! 🙂
