If you want to Find the WEP key, your best bet would be to connect via the Ethernet port on the router. Then log into the Gateway address, which on most routers is 192.168.0.1, or go to Start>Run> cmd, press enter, then type ipconfig /all .Take a look at the Default Gateway, note that down, then open Internet Explorer and type 192.168.xxx.xxx (replace xxx for the default gateway IP address). Log into the router, most defaults are admin as user and password as password.
Look in the router for Wireless settings/Wireless Security. The WEP/WPA/WPA II key should be in that section.