Another way to do it

I run Leopard on my unsupported G4's and I think it works great. Personally, I don't think there should be a mechanism to prevent you from installing Leopard on your computer, it just doesn't make any sense. My two unsupported Macs, an 800mhz Digital Audio/Quicksilver (DA computer, QS 733mhz processor, overclocked to 800mhz) and a 500mhz Dual Gigabit, run it just fine. In fact, there isn't much difference from Tiger. If anything I think the dual 500mhz runs BETTER with Leopard. So if you want to install it on your G3 266mhz iMac and have nothing work and blindingly slow performance, that should be your call. That said I'm all for programs like Leopard assist, which helps you get Leopard going on your unsupported Mac.