Hi, I've got a quick question about buying a new MacBook in an Apple retail store. If I want the MacBook 2.4ghz with 4 GB of RAM, does the store need to install that extra RAM, or do they have some machines boxed up and ready to go with 4 GB? And if they do need to install it, how long does it take? Do you need to pre order it, or can they get it installed same day? I'm wondering becuase I'd like to go pick up a new MacBook at the Black Friday sale tomorrow if the price is right. Thanks!