Even some 64-bit EFI machines won't run it, because they have Intel graphics. Anything with the 965 series (such as X3100) is unsupported for one reason - there was never a 64-bit kext for it. This is also what kept these machines from booting a 64-bit kernel in 10.7. So if Apple and/or Intel would actually create a 64-bit kext for the 965 series, a whole bunch more machines would run it just fine.
FWIW, this might also get your Mini up and running, as there are definitely ways to get around the 32-bit EFI problem. But until they create that kext (read: never), it's not gonna happen.