I'm confused. I have 1Gb (2x512mb) of RAM in there now. I want to upgrade to at least 2GB of RAM. My question is, do I need to buy 2x1GB of RAM, or could I buy a 2GB stick and replace one of my 512MB sticks to make it 2.5GB? What about one 4GB stick by itself? I know the maximum I can have is 4GB. My Macbook is the early 2008 model.