How do you measure the wind speed, im in the process of trying to make a cheap wind speed measuring instrument.
The Anemometer i use broadcasts the wind speed and direction for me. All i need to do is convert it from meters-per-second to miles-per-hour...
However.. the logic and mechanics are fairly simple. As the wind blows it pushes/spins the cups on the wind sensor. It uses either a Hall effect sensor, Phototransistor or reed switch to count the rotation of the cups. The faster the cups spin... the stronger the wind. The hard part is getting the formula that converts RPM to some type of wind speed (for example.. 1 rotation = 2.5 mph). It's probably easier/cheaper to buy a wind sensor that provides the formula.
My friend recently finished an Arduino project that captures and logs Wind Speed. He's using the data to help plan/build wind turbines for a remote cabin he's building. His project is documented here (w/ his Arduino sketch): http://blog.flgator.com/2010/05/arduino-wind-speed-data-logger/. IMHO, its a way more USEFULL project then my 'how hot is it in my backyard' weather station project 
~Brian