Assuming you are using the Verizon Actiontec router:
1) Log into the router
2) Click on Wireless Settings
3) Click on Advanced Security Settings
4) Click on the WEP bullet
5) You should see the current WEP key
6) You should now be able to go into the wireless setup on the PC and enter the WEP key there.
FWIW, WEP is not known for its great security. It is highly recommended to use WPA or WPA2 if you can (and that depends on whether all of your wireless clients support WPA or WPA2, the Actiontec does support both).
Hope this helps.