So what your basically after is a Service (Web, Game or whatever) that is online either by IP or Domain name to be on and if Connection A Stops (NTL) the ADSL Connection would take over. The Dual Head approach as far I understood at the time was bascially 2 x IP's coming in but you on the other hand only see it as one connection. Not sure of the router you have has the abilty to direct traffic to the other connection should one fail (as this is what your looking for) and then been port forwarded to your server machine.
Now the Network Gurus understand what your after, Im sure one of them can maybe point you in the right direction
