The model 1,1 (Early 2006) can use 2gb of 200 pin 667mhz PC2-5300 RAM The model 2,1 (Late 2006 & Mid 2007) can use 3gb of 200 pin 667mhz PC2-5300 RAM The model 3,1 (Late 2007) can use 6gb of 200 pin 667mhz PC2-5300 RAM The model 4,1 (Early 2008) can use 6gb of 200 pin 667mhz PC2-5300 RAM The model 5,1 (Late 2008, Aluminum Unibody) can use 8gb of 204 pin 1066mhz PC3-8500 RAM The model 5,2 (Early 2009, 2.0GHz Model Only) can use 6gb of 200 pin 667mhz PC2-5300 RAM The model 5,2 (Mid 2009, 2.13GHz Model Only) can use 6gb of 200 pin 800mhz PC2-6400 RAM The model 6,1 (Late 2009, White Unibody) can use 8gb of 204 pin 1066mhz PC3-8500 RAM The model 7,1 (Mid 2010, White Unibody) can use 8gb of 204 pin 1066mhz PC3-8500 RAM
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.