Aircrack can be used to crack WEP keys: http://www.aircrack-ng.org/doku.php AirCrack and all other wep cracking programs work by monitoring all incoming and outgoing data viewing the wepkeys within it until it has found enough to crack the wep key. When you are using the application ensure that you use it in busy hours when the guy is in. Office and company wep keys are easier to crack because of the amount of data traffic but a small building with one or two may take longer. Im sure the is plently of tutorials for it remember a wireless card is needed.
Scorpik