I currently have this configuration: 2.66 2gb ram 220 gb hard drive 320gb hard drive airport + BT extreme Newest firmware. I just ordered new ram from maxupgrades. 2gb. Received the ram and put in 1 stick on the top riser and one on the bottom riser and ran into this problem. It will not recognize by OSX or XP at all. (system profiler,...) I've tried these methods to fix it. Reset pram, msc, vram, i've excluded that it could be a bad riser slot by switching the ram around. I returned it back to the maxupgrades and he said the ram was working perfectly.