Hi I am planning on installing new memory in my Macbook, which I got in Dec 2007. I downloaded the Mactracker program to find out the maximum amount of memory I could install in the machine, and it says: "Maximum RAM: 6.0 GB Actual, 4.0 GB Apple" What does it mean by 'Actual' and 'Apple'? Can I install 6 or 4 GB? Advice would be much appreciated. Thanks!