I think I saw a book a few years ago on how to build your own mac from parts. But in general its not done. Of course you can hotrod most macs in various ways - ram, hard disks, video board, pci boards, monitors, internal optical drives. Usually the higher end macs are more configurable. I saw that the Mac Mini only comes with 256 ram - and it takes an apple tech to install more ram. what a hassle. apples are really not the place for building your own machine. but some people here use windows machines in conjuction with macs.
