http://itunes.apple.com/us/app/os-x-mountain-lion/id537386512?ls=1&mt=12

OS X Mountain Lion Specs;

Supported
Models

• iMac (Mid 2007 or newer)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• Xserve (Early 2009)

• MacBook Air (Late 2008 or newer)
• Mac mini (Early 2009 or newer)
• Mac Pro (Early 2008 or new