Well on my computer whenever someone wants the WEP key I click on the internet connections icon (the 5 bars thingy near the date, battery life and volume areas) -> Right click on the name of the wifi you're currently connected to -> select "properties" -> check the "show characters" box in the security tab which should pop up. It should reveal your WEP key/password.
This is on Windows 7(I think

), hopefully there is something similar on whichever OS you're using.