Rui CarmoLeopardAssist is an Open Firmware tweak that allows you to set up Leopard on older PowerPC Macs, including the 700Mhz dome iMac (which is where I’ve done it twice so far).
Since it is so absurdly useful to breathe new life into older hardware, I am mirroring a copy of it here (if you use it, make sure you run it from an admin account).