Mountain Lion is scheduled to hit shelves in July, but it seems that several early Mac models won’t be supported by the new operating system.
This is bad news for older Macs but I think it good to change your computer now. Maybe OS X Mountain Lion cannot handle low specs of Macs anymore. Now, they just release new Macbook Pro with retina display.
According to Apple’s official software upgrade guidelines, you will be just fine if you are using one of those:
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)
Before you upgrade, you need Snow Leopard or Lion in your Mac. If you are running Snow Leopard (10.6.x), update to the latest version of OS X Snow Leopard by clicking Software Update to install Snow Leopard v10.6.8, the latest version. More info to upgrade, click here.