There are many great FOSS projects that utilise old PC hardware and give it a new lease of life. The best is desktop computing with various Linux distribution flavours like Mint, PCLinux, Ubuntu and countless others. In fact it is my considered belief that the best hardware to run Linux on is infact (almost) any machine that is at least 12 months old. It is possible, of course, to select components based on the degree (and maturity) of the specific support under Linux but this has two major drawbacks.