If you are trying to connect wireless that WEP key is they encryption key any wireless device will need to connect to your secure network. Meaning whatever wireless source you are trying to get the signal from.
A little more detail about the setup may help.
1. Where is the source that this wireless card will get it's signal from
2. If it is a router on another PC then that is where you would have to go to find what type of security it is running and what they key is. It would be in the routers wireless settings.