In addition to dual CPU's and cooling stacks, you'd need a replacement fan assembly (the single processor 1.6's and original 1.8's have only a single fan forward of the CPU; the duals have a double fan). I recall reading somewhere that going to dual CPU requires soldering/desoldering some jumpers on the motherboard, so any such future upgrade would undoubtedly void any remaining warranty (e.g. AppleCare). Can't swear it's so, though. Joe Gurman -- "I love deadlines. I love the whooshing sound they make as they go by." - Douglas Adams, 1952 - 2001 Joseph B. Gurman, NASA Goddard Space Flight Center, Solar Physics Branch, Greenbelt MD 20771 USA