I'm puzzling with the thought of upgrading the memory from 2Gb to 4Gb. I have the "old" 24" iMac. In the Service Manual it says I can install 4Gb, but the system supports no more than 3Gb. I was wondering, when they say "system" is that the hardware, or the OS? If it's the OS, will Leopard support full 4Gb memory? Or anything beyond that for that matter, now we're hovering around the subject..