First we need to know which one of the 9 different models of MacBook you have. To see which model you have go to the Apple in the upper left corner and select About This Mac, then click on More Info. When System Profiler comes up check the Model Identifier and post it back here.
The Early 2006 model 1,1 Core Duo can only run a maximum of 10.6 Snow Leopard.
The models Late 2006 Core 2 Duos 2,1 through Early 2008 4,1 can only run a maximum of 10.7 Lion.
The Late 2008 model 5,1 Aluminum Unibody through the Mid 2010 White Unibody model 7,1 can run 10.8 Mountain Lion.