Step 1. Tell him to throw away his Mac and get a PC. (A whole Mac is almost as evil as the Windows OS)
2. Format your hard drive and your friend's.
3. Install Linux on both machines.
4. Learn to use and love the penguin.
5. Read the the following howtos, particularly the first one.
http://howto.x-tend.be/openMosix-HOWTO/
http://www.ram.org/computing/linux/linux_cluster.html
6. Enjoy your new Linux cluster that automagically detects new nodes on the network.