I must say, I wish we'd had the time to get our own version done first and who knows what may be yet... but this is here now and it works now to the t.
As some of you already know, although Leopard 10.5 will not install on a Mac with a processor of less than G4/867MHz - even including DUAL 800MHZ G4 - there are other routes like target disk mode, cloning, etc - to get it on those systems and it runs JUST FINE. The 867MHz cut off is a soft cut off, and it's one that can be worked around.
You still need a DVD drive to load the Leopard DVD. A Quartz Accelerated AGP video card (anything better than the non-accelerated ATI Rage Pro if you've got a PowerMac G4 is an option providing a night and day difference) is of significant benefit. This also doesn't change that the Mac must be a model with a G4 processor and Bootable FireWire port... that includes all G4 PowerBooks even the Pismo with an upgraded G4 processor, PowerMac G4 AGP Sawtooth and later, but excludes The G4 PCI 'Yikes' just the same.
To the point – You can fake out the installer with Open Firmware by following the instructions here. The Leopard installer see your Mac as having a processor complying with the 867MHz min. For those of you with an AGP Mac, as previously covered - you can have your cake and eat it too by upgrading to an actual faster processor which negates this app need + gives you faster system speed. But if you've got an iMac G4, Powerbook G4, or eMac G4 - that's not even an option. So by utilizing Leopardassist, you can now directly install and reap those benefits that drive the desire for Leopard in the first place. Enjoy. :)