I have a Dell Dimension 4600 that has 256mb of memory and I wanted to add some more. It has 4 slots: 1 and 3, a small gap, then 2 and 4. There is a 128mb in slots 1 and 2 for the 256 total. I was thinking of adding 512(2x256) on top of that, so would I put the new ones in 3 and 4, or would I move the 128's to 3 and 4 and put the bigger cards in 1 and 2? I'm not sure how this memory configuration thingy works, someone said it's ok to have different sizes and I read somewhere else that it's good to have 2x256 rather than one 512 card by itself. Does anyone know of a good place to pick up memory? It seems cheaper online from the sites i've seen, but I know nothing about the brands or quality. I suppose I could add 2x512mb instead if my computer will allow it, 256 just doesn't cut it for multitasking.