is this a good deal? I'm interested in upgrading my memory in my 2.4Ghz MBP. At apple.com it's $400 for 4GB, I found a place online that's $79 for 4GB, and at Best But it's $200. How is this possible? PC2-6400 800/667/533MHz I'm overwhelmed by the jargon. I want some memory that works and will result in a noticeable increase in performance. Where should I go? Thanks!