Mini-ITX is a recent standard for miniature PC motherboards. Each is about the size of a 7" single, typically uses little power (often not needing a fan), and has everything from Ethernet to video to the obligatory USB and FireWire on the board. People have been using them to build
all sorts of projects, from battery-operated Linux-powered robots to DIY consumer electronics, to modern PCs embedded in everything from bakelite radios to Commodore 64s.
http://www.theage.com.au/articles/2002/06/20/1023864460978.html