The mini is by far the easiest because the CPU is in a socket, and is relatively simple to get at. Unplug the old processor, and place the replacement in the socket. Apple's laptops all use soldered-in processors, so upgrade will not be possible for the home user. The iMac also has a socket, but is much more challenging to replace. In fact, I don't recall seeing any articles where someone has replaced a processor in an iMac. The MacPro is considered upgradeable, too. The MacPro processors are much more expensive than the Core2Duo.