Your average Joe doesn't need to do anything in particular to change their ip address. Since most internet providers use DHCP, the user is given a new ip every time they log on. If they have have a broadband connection, they still have a dynamic ip but they may have the same one for a few weeks or a few months. Some times just rebooting the gateway/modem will give them a new ip address. In short, banning a specific ip address will not do you much good because the user will just get another one. You can block a range of ip addresses but that could eliminate innocent users from that service provider. The best way to prevent this abuse is to require a user name and password before anybody can post or do asnything on your site.
