I've got my dual 500 MHz 'Mystic' Power Mac G4 running Mac OS X 10.4.11 - just like my main Mac, a dual 1.6 GHz upgraded 'Digital Audio' Power Mac. The Mystic has a 17" Samsung display set at 1280 x 960, and to the right of that is the Dell flat panel display connected to the Digital Audio.
I've installed Teleport on both, set Mystic as a "shared" Mac, and now I can simply move my mouse from one display to the other. The keyboard works with whatever screen I'm on at the moment. Very cool! I can drag files from one Mac to the other by dragging them from one display to the other, and I have it set to synchronize the clipboard, so I can cut-and-paste between machines. (For some reason, it's only working in one direction - from the master to the slave.)
My goal is to do this with Leopard on one Mac (most likely the upgraded Digital Audio) and Tiger on the other (Mystic right now, but the dual 1 GHz 'Mirror Drive Door' Power Mac when the quieter cooling fans arrive from NewEgg.com). This will let me migrate to Leopard as my main OS and still be able to use Tiger and Classic Mode as necessary. (Yes, after all these years I'm still using Claris Home Page.)