how to find WEP/WPA key to network if possible

[Antonio Olivares]

Dear all,
How does one get a KEY to a secured network that could be WEP/WPA?
Why we had a unsecured wireless network at school and I could connect with a laptop.  Everything got configured automatically, now, the computer does not connect automatically.  It is asking for a KEY and I do not know the key.  The Network Administrator is hard to find/on vacation.  Is there a way easy/hard to find the key so that I can connect to this network?  
TIA,
Antonio