If you haven't set a WEP code and you are with sky/BT or someone, check the label under your wireless point, the WEP code is often printed on there.
I haven't heard of wifi routers supplied with WEP codes already installed.
it should be 10 characters, you need to put it all in
If it is the wep key it'll say WEP:10characterwepkeyhere
If not, then you need to ask whoever set up your wireless point/check the documentation that came with it.