Currently Being ModeratedFeb 4, 2013 10:34 PM (in response to runner_pucci)
Welcome to the Apple Support Communities
You are using OS X Lion, and Messages (with iMessage) is included on OS X Mountain Lion.
If you bought the computer recently, see if you can upgrade to OS X Mountain Lion for free > http://www.apple.com/osx/uptodate
If you can't upgrade to Mountain Lion for free, open App Store and purchase OS X Mountain Lion. Make a backup of your files before upgrading