LeopardAssist

LeopardAssist is a simple tool to install Leopard on older, unsupported Power Macs.
It bypasses the 867 MHz processor check in the Leopard installer to allow systems that don't meet the requirements to complete installation.

It achieves this by temporarily faking the clock speed in the device tree, changing it to 933MHz, and then launching the Leopard Installer. No modified Leopard DVD's, no hardware hacks or tweaks, just a one-time run application. (Much like XPostFacto)
This application is not required on the majority of systems with processor upgrades that already have their processor speed bumped beyond the 867MHz cutoff point. As such LeopardAssist was not built to factor in these upgrades.
LeopardAssist is a free but discontinued tool. Support was discontinued in mid-2009 and the application is no longer updated now with the release of Mac OS X Snow Leopard.