i have a mandrake box running my NTL connection, basically on NTL what you need to do to get it working properly is the following:
plug everything in, make sure everything is connected etc
2: switch off your set-top-box, wait ten seconds and plug it back in
3: when the box has stoped flashing, the internet part is ready, however, NTL insist that your NIC's MAC address is registered with the ntl system. so during this initial power on period you have 10 mins to accuire an ip address on NTLS broadband setup system thing, if you dont you have to go back to step 2 and start over.
you can get an ip address by using your favorite dhcp client, when you are configured your ip address will be either a 10.x.x.x or 172.x.x.x range.
4, Follow on screen instructions and add your computer to the list, your account password and account number can be found on your initial welcome letter, if you have lost it you can phone the customer services number and ask the nice people for it.
5, when you have reached the end of the setup, where it says 'now follow the instructions on the back of some leaflet to the letter' ( in RED ). you need to unplug your Set-to-box again, wait 10 secs and plug it back in
6, once again, once it has stoped flashing, request an ipaddress using your dhcp client, and presto you should be up and running. once you have requested your ip address the dhcp server will not accept any new request until the set-top-box is power cycled again. when you have your final ip address it will normall be in the range of 213.x.x.x depending where you are in the country etc. NTL say these ipaddress are dynamic, however i have found its bound to the card whos MAC address is registered, i found out because i took my laptop to a friends house pluged it in and got my ipaddress
then on my linux box i have my iptables setup to forward the traffic properly, and i run named ( a dns server ) basically it acts like a DNS proxy to anything that sits behind your linux box. then on your client pcs set your dns server to your linux boxes ip address and the default gateway to your linux boxes ipaddress.
if you get stuck, post back here and i'll help you
oh BTW, at the time of this writing: yesterday a bug was found in ssh that could lead to a root level compromize to your system, redhat have released a patch already, however on systems you yet cannot patch it is recomended that you only allow known traffic to your ssh server or stop it altogether by shutting down the service or adding in an iptables rule to block it from outside.
the above is just a warning, dont panic like i have seen some people do