I use NTL cable via a set top box. Normally you connect direct to the Internet. I take it you have checked in both the browsers to make sure they are set to connect directly to the Internet and haven't got a proxy address?
Try IP chicken click here and under Advanced see what the Name Address says, it should point to your local server.
I do use a proxy sometimes if I have problems with my local server not allowing me to access some web sites.