Sounds familiar!!
LOL
Anyhow to answer your question, yes it is possible to ban users by IP address but.... 2 main problems
Most internet users have a dynamic IP address, this means that their IP address is assigned to them, when they connect, from a pool of addresses owned by their ISP, so if you ban their IP all they have to do is turn their router off and on again and they get a new IP address.
the other problem that banning IP's can cause is when you are dealing with large companies or universitys where you might have hundreds of people all accessing the net through one common connection, in that situation evey person using that connection would appear to the outside world to have an identical IP address, so if you ban that address you maybe banning several hundred innocent users.