Thank you for all the foregoing excellents posts. This is how I got on:
1) I connected the cable modem to my laptop via a standard ethernet cable.
2) I powered on my laptop, opened internet explorer, put in the address bar: 80.5.178.26 and was immediately logged into
http://autoreg.autoregister.net/
3) I followed the NTL prompts using the previously supplied customer details, pin number etc
4) I decided to go for the NTL approved Actiontec Cable Router & USB wireless adapter bundle - currently £99.99 inc. vat & next-day delivery. The reason I chose this rather than the excellent idea of "kfridge" (previous post) was that a USB adapter has greater signal pickup over a PCI internal ethernet card.
5) I went to the outlying PC and plugged in the USB wireless modem and XP picked it up automatically.
6) I used XP's own software for Wireless networks rather than Actiontec and connected without trouble - given the location of the cable modem downstairs in one corner of the house and the PC in the upstairs opposite corner - the signal strength was "very good"
7) On the PC, I accessed the Actiontec Router by putting into Internet Explorer its IP address 192.168.0.1. There I setup 64bit WEP making up my own Hex code - there's an example showing in the Actiontec CD manual. The Router was rebooted and the connection was lost.
8) When the Router came nback online, the PC flashed in the lower right-hand corner, that there was a wireless network available. I put in the Hex code and "Bob's your Uncle"
The above steps might seem off-putting to some, but they are really quite easy as it's mostly intuitive - thanks to you guys for getting me on the right start.
Cheers all.