I don't think it is an account ID as such, but, TBH, to be able to get any useful information from it (even if it is), a hacker would need access to NTL's systems. If they have access to NTL's systems, they have access to information whatever NTL put in the DNS entry. This is the same with ANY IP, from any ISP. It's also worth noting that ANY broadband connection will have an IP that can be associated with it.
incidentally, you can get the information yourself without going to a website. Assuming you know your own IP, just type "ping -a <yourip>" into any command prompt.
Update: Look at
http://homepage.ntlworld.com/robin.d...e.html#dnsname for details of how to decode your NTL DNS Name. It doesn't contain a reference to your account.