[ladyada] ran across this excellent hack by [phillip]. Apparently there's a clock, data, 5v and ground connection available in most modern video connections. (He even notes HDMI cable pins) He wrote some drivers and can now control i2c hardware directly from the PC Mac. [Ladyada] notes that most laptops use an i2c bus for extra sensors as well. For now, the code only works on Mac OS X.