I am hoping to buy the new iMac when it comes out. I am looking for advice on the best ( cheapest) way to get a decent amount of ram. It seems that crucial is a good place to buy ram. Do I have to buy the extra ram in the same size units as the one that comes with the iMac. Say as an example I want to end up with a gig of ram. What is the best size unit to order with the iMac so that I can buy most of the ram from crucial? Does putting in extra ram yourself affect the warranty? Thanks for any help.