Techradar posted a story that Apple has confirmed on its official Mountain Lion upgrade page what was rumored back in February - older Macs will not support the upgrade despite being 64-bit systems
The list of supported systems includes:iMac (Mid 2007 or newer)MacBook (Late 2008 Aluminum, or Early 2009 or newer)MacBook Pro (Mid/Late 2007 or newer)MacBook Air (Late 2008 or newer)Mac mini (Early 2009 or newer)Mac Pro (Early 2008 or newer)Xserve (Early 2009)Older 64-bit Macs won't get new version of Mountain Lion
