WepAttack is a WLAN open source Linux tool for breaking 802.11 WEP keys. This tool is based on an active dictionary attack that tests millions of words to find the right key. Only one packet is required to start an attack.
with wlandecrypter is a good combination to break WEP keys in minuts. With only one packet you can get the password:
wlandecrypter bssid essid | wepattack -f file.cap
like I explain at the post http://behindmaemolines.blogspot.com/2007/11/wlandecrypter.html
The bad thing is that wlandecrypter only goes in SPAIN with telefonica routers.
I didn't tested yet, any suggestion feel free to comment.