I just bought a new Mac Mini today (yes it took me forever to finally give in). I can't afford to buy 8GB RAM right away, but it seems wasteful to me to buy 2 2GB stick and then replace them later. Can I buy 1 4GB stick and add it for now and then another later? Pardon my RAM ignorance. I've always had Dells that need to be replaced in pairs, but am hoping this my be different. Thanks!