Like pipes said, if you search an IP (provided you have the account to do that here) in the MPi, it will show who has used that IP and if it is associated with a ban. Now the thing you have to keep in mind, is that IPs swap around quite a bit and can go to many different players. So the key is to look at any ban in question and then get the information on the ban...like the date, time, server and so on. Now take that information and look to see if the player in question actually was using the IP at the time of the ban. Just because a player has used an IP that has a ban associated with it, does not mean they have cheated, it is just a stroke of bad luck for him.