what wifi adapter are you using? is it plugged in to the pi or to a usb hub? is there an led lit on it?
i have this guy
and it's got a blue led that's on solid if it's powered but not configured and blinks when it's working.
do you see the device when you type lsusb at the command line?
"If I had known it was harmless, I would have killed it myself." - Phillip K. Dick, A Scanner Darkly