(POE) allows users to mount an AirPort base station without a nearby electric power outlet. The updated version now uses a compact cable assembly approach, allowing users to use any Ethernet cable to carry power to the Base Station--up to 250 feet away for AirPort snow (Dual-Ethernet) and 150 feet away for AirPort graphite (Single-Ethernet). A pair of adapters carry the DC power in the data cable. It is $30 (but does not work with Airport Extreme, which the company says it is now designing).
http://macwireless.com/html/products/accessories/poe.html
http://macwireless.com/html/products/accessories/poe.html