An IP ban wouldn't really be useful unless he has a static ip, in which case he would simply have to disconnect and reconnect to get a fresh new ip... thus ip ban circumvented.
Depends on the ISP. Cable connections are always up, therefore, the chances of getting a new IP address after resetting your modem or PC are very small. DSL connections are up and down unless you're connected through a router and more than likely will change each time unless you authenticate with a static IP. Forget about dialup isps