It appears that, 'AppleNForceATA: found 0 units.' may not be the problem after all: I'm currently stalled trying to boot on my Snow Leopard disk with the following error: 'dyld: shared cached file was build against a different libSystem.dylib, ignoring cache'. Now it's possible that AppleNForceATA is still the culprit because above that message is the same, 'found 0 units' message twice. So far I'm stumped. I'll try taking out my GPU's EFI string and see what happens…