I have the base 21.5" iMac (because hey, if I'd have got a machine with these specs six months ago, I'd have been paying $2400, graphics card aside, which I don't need for anything I do) and no matter what I do, I CANNOT get it to boot in 64-bit mode. Tried holding down 6 and 4 (unlikely to work since it's a BT keyboard after all) and tried modifying the boot plist. Still nothing. The Terminal command to check 64-bit extensions returns that it SHOULD be okay, but it says 64-bit extensions "no" in System Profiler. What gives?