
to CF
How are you connected to the internet?
The Linksys router is a 'cable' router and the BT device is an ADSL router! Have you got the PC plugged into the Linksys (via RJ45) and then a wireless connection between the two routers with an ADSL line to the outside world?
As the pages linked above say, the Linksys router admin is on 192.168.1.1 and iirc by default it is disabled for wireless connections - ie you need to plug a system into one of the rj45 ports to configure it.
The BEFW11S4 will only support WEP encryption, which is very weak, and SSID hiding doesn't add much to security (and may cause contention problems).