well if i upgrade my old stick (256 DDR 333) to say the same as the other one (512 DDr 400) what improvments am i making with having two of the same? oh and i used a program (belarc advisor) to tell me the stats of my computer, and it says i have 4 DIMM slots, these are Ram slots rite? well wen i open my computer i only see 2? thanks.