Thanks, XXXXX XXXXX the only info I need. The problem is, you are using Mac OS 10.6 Snow Leopard and the update you downloaded is for Mac OS X 10.7 Lion
10.6, 10.7 and 10.8 are the Major OS X versions and 10.6.1, 10.6.2, 10.6.3, 10.6.8, 10.7.1, 10.7.2, 10.7.3 etc are the minor updates for the OS Xs. Minor updates of one version of OS X can't be installed on other Mac OS X versions.
I mean updates of 10.7 Lion can't be installed on 10.6 Snow Leopard
Basically, 10.7.1, 10.7.2, 10.7.3 etc are the minor updates of 10.7 Lion and can only be installed if you are running 10.7 Lion. In the same way 10.6.1, 10.6.2, 10.6.8 etc updates can only be installed if you have 10.6 Snow Leopard installed.
Your Mac is capable of running the latest Mac OS X 10.8 Mountaion Lion. I'd recommend to upgrade your Mac OS X from 10.6 Snow Leopard to 10.8 Mountaion Lion. You can run all OS X 10.7 application on 10.8 Mountaion Lion too
You can buy Mac OS X 10.8 Mountaion Lion from AppStore (as digital download) for $19. See here : http://www.apple.com/osx/
You can find the AppStore application in the Applications folder.
Please let me know if you have any questions. Don't Rate my answer until you are satisfied.