Hello all. I need to install more memory on an old dell 4600. At the moment it has a pair of 128mb pc2700 cl 2.5 modules. I ordered a 512mb pair with the same specs. I know that each module in a pair should be the same, but do the pairs have to be the same also? One other thing. Should the larger memory pair go in slots 1 and 3 where the current 128mb pair is or just put them in 2 and 4? thanks