WEP security over wireless network

i have got an unsecure wireless network set up, i would like to find out how to set up WEP to secure the network.
all systems are running Windows XP Pro SP2. i have got a wireless adsl router - D-link D604T, which supports WEP, and all pc's have either a Belking wireless network card, or a d-link wireless network card. all support 64, 128 bit WEP encryption, but im not too sure how to set it up.

i have logged on to the router, told it to use WEP, and what key to use, but when i tell my network cards to use the key, they wont connect to the router.

can any one tell me how to sort this out. thanks

 

You have to set the Router first and the setting has to be identical.