Whatever you do, don't use OCZ RAM.
Put on a pot of coffee, throw some good music on the stereo, curl up in front of your computer with a blanket and search the forums here, at HardOCP and at Madonion (and probably more) for "OCZ" . You'll have quite a bit of reading to do. The vast majority of it will be from people talking about what a rip-off OCZ RAM is.
I've never used Apacer so I can't comment on it.
I'd reccommend Corsair XMS2700, (real) Samsung PC2700 or Mushkin PC2700 RAM.