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10.6.8 is an update for Mac OS X Snow Leopard, and you are running Mac OS X Leopard. First of all, you have to upgrade to Mac OS X Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard

Then, before upgrading, make a backup of your data with Time Machine and/or Carbon Copy Cloner. After doing this, insert the Snow Leopard disc and upgrade.

The DVD will install Mac OS X 10.6.3, so open  > Software Update and install Mac OS X 10.6.8

Mar 14, 2013 11:20 PM

• Ernst, Edzard (November 2005). Retrieved 2008-02-01. Serial dilution lab conclusion.