yes, it is possible, if you are a computer technician and know the basic skills about computers and how they operate... or a genius hacker
did you know way back when, computer hacking was pure? nowadays it is all about hacking into the system and thinking "what kind of trouble can i cause?" or "how can i get into this persons personal data?"
You can crack a Wi-Fi code, but this is only possible when the end user has a weak code. To crack the code, you will need a compatible wireless adapter, a BackTrack Live CD and, of course, a WEP-enabled Wi-Fi network. Check out the procedure on lifehacker.com/5305094/how-to-crack-a-wi+fi-networks-wep-password-with-backtrack.