Installations (both you tried) doesnt have support for you chipset. Search on the net, wiki is an option too, how to inject driver into installation DVD, you'll need a working OS-X, or TransMac to do it via windows. First do some research to find relevant driver for you nforce chipset then you'll have to inject it. It's not very difficult but requires some work and effort. Have in mind, when you successfully inject chipset driver and install Leopard, the installer will not copy chipset driver into hdd installation (injected one will be used just for the dvd, to boot and install osx, it will see your hdd's, usb, etc). So after installation you will have to boot with dvd again, and copy that kext into hdd leopard installation.
Good luck buddy !

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