|MadSci Network: Earth Sciences|
There are plenty of web sources which show you how to build homemade weather instruments. Check this site for some pointers on building a simple barometer and anemometer, or this one at the Canadian Weather Office. NOAA has a pile of weather-related experiments for kids. Go here for experiments related to wind and temperature. The Yahooligans for links which will take you to other weather tool sites.
Try the links in the MadSci Library for more information on Earth Sciences.