Boot to original or Snow Leopard install disks (or other volume).
This system can run the last version of OS X 10.7 "Lion" if upgraded to at least 2 GB of RAM. Although it has a 64-bit processor, it has a 32-bit EFI and cannot boot in 64-bit mode. It also does not support "OpenCL" running the default video card or the other build-to-order video cards that were offered via custom configuration.
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