Late mail:
I just played around with some DNS lookups on AO Hell hostnames and it seems that the HEX coding does relate directly to each octet in the users IP address so the above banning method should work in many cases. The thing with dynamic IPs is that the third octet as well as the fourth can sometimes change too (ie: when the luser that got banned redialls). The method used by AO Hell to generate hostnames is not really helpful as ultimately you will end up banning more people than who deserve it, but then again not all your users will be on that ISP so it may not necessarily be a concern.
