I was getting along pretty well with the 2X512Mb RAM modules in my MacBook C2D. Recently I also bought a refurbished iMac C2D that came with a 1X1Gb module. I upgraded the iMac to 4Gb (Crucial). I took the 1Gb iMac Hynix module and put it in the MacBook giving me 1.5Gb. It worked fine. I then picked up another 1Gb Hynix module off eBay and put it in my MacBook for 2Gb total. Works fine. I also upgraded the original 80Gb HD to 160Gb. Putting the old 80Gb HD in an external USB case made data migration pretty easy.