The full instructions for your router, in PDF format are here:
http://kbserver.netgear.com/pdf/wgt6...al_25Apr05.pdf
But, in stages, plug your NTL cable modem into the inter (wan) ethernet socket, and then, if no wireless adaptor bought yet for your 360, use ethernet cable to connect from rear of 360 to ethernet socket one on the netgear router.
When I was with NTL, I used the Linksys router, and found it so easy to set up, but reading the specs on the Netgear, there should be no problem setting that up to work too, so read the setup info slowly, and report back if you're still having problems, and we can go into more details, stage by stage with you.