ah but if you just delete them they can rejoin under a different name and continue, once deleted you cannot find their ip address, their email or any other information, to stop them returning you need to add their details to a blacklist that the forum will compare every new user against, which will mean that their ip address, email etc cannot be used again to register on the forum.
there are a lot of little things that moderators and the admin do for a forum that goes on behind the scenes, depending upon their user rights, one forum was set up so that only the admin could ban the users and add their info to the blacklist, so all spammers posts were dropped into quarantine and their posts set to moderation, so they couldnt post anything new.
actually setting the so they cant post but not deleting their account can sometimes prevent them re registering again - depending upon forum settings.
Grendel