i'm going to upgrade the memory in my desktop computer from 128mb to 512mb. i know which memory i need and how to do it (i read about it quite a bit). i just have two questions... my computer has two memory slots. right now the 128mb is in one slot and the other is empty. would it be better to put a 512mb in the slot where the 128mb is and still leave the other one empty? or would it be better to put a 256mb in each slot? does brand matter for the memory? i hear kingston is pretty good but it's expensive. i don't know much about the brand names so they're all the same to me... thanks for any assistance p.s. - i'm running windows xp home on a hp that's about 4 years old.