How do i find my "SECURITY KEY" or "PASS PHRASE" for my new laptop's internet?

How do i find my "SECURITY KEY" or "PASS PHRASE" for my new laptop's internet?

i have linksys on my other laptop and i want internet on my new one but i dont know what the security key or pass phrase is. where can i find it. my new laptop is a windows vista and the only way i can connect wireless is to put in the password thing.
please help cause i have no idea where to find it. if you need ask for me for more questions and stuff , no matter what it takes to find the answer/password!!...