Tried it on a G4 450 with PCI Radeon Mac Edition + 1GB RAM. It ran like an absolute dog compared to 10.4. It's not especially fast on my 1.33 Ghz G4 and that's way above the specs of the machines you're thinking about. There are also reports of GPU's that don't support Core Image (like your Radeon 7000 and I'm guessing the Tibook has a Radeon 7500) not running Time Machine properly or at all. To be honest mate I'd stick with Tiger or you'll be in for a very sluggish experience.