Sorry if this is a bit off topic, but how does the 5,2 MacBook only have DDR2 667 MHz RAM when the 5,1 comes with DDR3 1333 MHz?
Easy answer.
The Macbook5,1 is an aluminum unibody, with a lot of changes, such as Mini DisplayPort, and a multi-touch trackpad.
The MacBook5,2 remained with the older style white polycarbonate case, along with the older memory bus, basic trackpad, etc.
I thought the 5,1 SHOULD have been named a MacBook Pro, as it would fit in better with that line. I couldn't tell you why Apple decided to leave it with the MacBook name, other than the 13-inch screen size. The 5,1 was an additional model, while the 4,1 was slightly upgraded, but continued to be sold. The 5,1 was "replaced" by the MacBookPro5,5 model. The 4,1 continued on to the 5,2 with the older MacBook "features", along with keeping the DDR2 for another year, when the Macbook6,1 was released with DDR3.