Firstly, I assume that it is NTL's *CABLE* broadband service that you have, because NTL provide both Cable and ADSL services? The WRT54GS is suitable for Cable broadband - I have the same router connected to Telewest's Cable service.
Despite the dire warnings to run the CD first, I deliberately set mine up without using the CD/wizard and it worked first time. When I subsequently ran the wizard to "try it", my internet connection stopped working. I "reset" the router and set it up manually again.
Power everything off, including the Cable Modem (or Set-top box) which should be left without power for a couple of minutes. Connect the router's WAN (internet) port to the Cable Modem's ethernet port and the PC to one of the router's LAN ports, both with standard ethernet cables.
Power on the Cable Modem and wait for it to boot fully and be online. Then boot the router, wait for it to boot fully with steady "power" light and active "internet" light. Finally boot the PC.
The PC should automatically get an IP address from the router in the 192.18.1.xxx range. Typing the router's own IP address of 192.168.1.1 should let you access its Setup pages, after entering the default password of 'admin' (all lower case and no Username).
In the Network Connections folder, if the PC's "Local Area Connection" hasn't got an IP address in the 192.168.1.xxx range - see screenshot: click here you may initially have to allocate a fixed IP address. (NOTE: Screenshot was with a different router which used "11" as the third part of the IP address, the Linksys uses "1".)
To allocate a fixed IP address, right click the Local Area Connection, select Properties, highlight the entry for "Internet Protocol (TCP/IP)" and click the Properties button. A box like this will open - click here (Ignore the red reference to DNS addresses, the picture was used in an earlier discussion.) Click "Use the following IP address" and type in:
IP address - 192.168.1.5
Subnet mask - 255.255.255.0
Default Gateway - 192.168.1.1 (the Router's IP address)
DNS Server address - 192.168.1.1 (the Router's IP address)
Leave the second DNS entry blank. Click OK back through the boxes.
You should now be able to access the router's Setup pages. In the first page, all you should really need to configure is the "Connection type" as "Automatic Configuration - DHCP". click here That should get you online with any computers that are plugged into one of the router's LAN ports.
Get that working and the next part is to get wireless connections sorted out.