Hi Marc, Congratulations on the Clamshell, I have the same type (graphite). As far as I'm aware, yes they can take 512Mb DIMMs. The same size memory module as the original Bondi Blue iMac, though I have a 256Mb stick in mine and haven't yet run out of memory when using programs. Hard drive noise varies with each machine. If you took 5 iMacs from the same line, I bet all their drives would sound a little different, even though they are the same model and same size hard drive. The iMac I'm using to type this on is fairly quiet, but my Sister's iMac is a little louder. Luck of the draw I guess. The hard drive on my iBook is reasonably quiet, just the clicking of the heads as they park. The only thing I don't like about the drive (apart from wanting more space, but who doesn't eh?) is the pause between operations on the screen, which I understand can be cured by purchasing a better internal drive. For example, I think the iBook 466SE's standard internal hard drive is a 4200rpm 10Gb drive. Well nowadays you could replace that with a lovely 40Gb 5400rpm drive with fluid dynamic bearings to make the drive quieter in its operation, and I nice memory buffer like 8Mb and faster seek time than your current hard drive. Second to memory, this would be the biggest improvement you could make to your Clamshell, and in my opinion, a clamshell with 576Mb and a 40 or 60Gb smoooooth hard drive would be a thing of considerable beauty.