(There's no video for Classic Environment for Leopard (9A241) yet. Please contribute to MR and add a video now!)
With the beta (9A241) OSX 10.5 Leopard build, it seemingly is possible to use the Classic Environment (Mac OS 9), a feature that Apple had removed in official OSX 10.5 Leopard builds.
To make this hack work, you will need to install Mac OS X 10.5 Beta (9A241) and then replace your OSX 10.5 (9A241) Classic Startup app located in /System/Library/CoreServices/ as well as replace your OSX 10.5 (9A241) located in /System/Library/PreferencePanes/Classic.prefPane with the ones included in this download.
After copying the System Folder included in this download to your hard drive, open Terminal and run these commands:
(122.05 MiB / 127.98 MB)
Mac OS X 10.5.x
Emulating this? It could probably run under: QEMU