Here’s the list for compatible model and year:
- 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)
A good list of compatible and incompatible apps is maintained in a searchable database by RoaringApps, check it out here.
Then, most important is Backup! Backup! Backup!
Once everything done,
Buy & Install,
Remember, if you bought a new Mac recently, Mountain Lion is free for you.
Also, if you are familiar with Mac OS X, strongly recommend you install with usb thumb disk as following step.(updated! new easier way to do same thing)
Get the newest version of LinoDiskMaker free from the developer