We previously reported that Mac OS X 10.5 does not support the Classic (Mac OS 9 runtime) environment for PowerPC-based Macs. The only option for running Mac OS 9 applications after updating to Leopard is to boot your system into Mac OS 9 (if it supports the OS) or booting into a Mac OS X 10.4.x or earlier volume.
Apple has now confirmed this information with a Knowledge Base article that states:
"Classic applications do not work on Intel processor-based Macs or with Mac OS X 10.5. Upgrade your Mac OS 9 applications to Mac OS X versions. Check with an application's manufacturer for more information."