Ouch . My ears..................
Best shot for the money.....FREE....Go get Zone Alarm..... (Sygate is good as well, more configuration options if you are so inclined)
As well make sure your AV is up to date and clean that system out. You may have a trojan sending this person your IP everytime you sign on. As well, take a good look at the people on your AIM buddies list. Tools are available that they can get your IP while AIM is logged in and proggies that can be used to punt you. Or switch to the secure chat feature.
Good luck.... :D
"Smile, and the world will smile back, or a least give you a silly grin"
anti-hackers first reason...lose the aol, couldnt agree more