Hello Everyone!

I have ubuntu 11.04 and I've been trying to connect to my university's wifi but it asks for a CA certificate( which is a .pem, .arm, .der file extension type) and I don't know how or where to get one. I mean, I downloaded two different types. One is a GeoTrust and another is an Equifax but I tried using both and it still will not allow me to connect.
I'm wondering if anyone can help me out? thanks! :] I'm pretty much a noob to ubuntu and linux.