Not that I am unsympathetic with your problem, but this is exactly why we advise people not to involve themselves in Fserve's, XDCC issues and mass/illegal file trading at all. You are liable for being infected with a virus, and the people that hang around in those kinds of communities are lamers who delight in nothing but exploiting someone's computer or in some way harming their Internet connection or PC (on top of evading bans, being rude to those in authority "just cuz they can" and generally making a nuisance of themselves). If you stick to using IRC for chatting, which is what it's meant for, then it's more likely you'll avoid these situations (but of course not certain).
As for your problem, make sure you're free of infections by using some of the following:The Cleaner
(Online virus scan)AVG
All of the above are free to use or try. You may indeed use them all, but make sure you don't use them at the same time as they may interfere with each other.
You might also like to put Norton on it's very highest and most sensitive settings for now. Furthermore, there is a blocking feature on Norton Personal Firewall which terminates all outgoing and incoming connections. This will cause you to disconnect, but it might help prevent the person hacking you if that is indeed what they are doing.
If it detects any IPs, you can also block them from connecting to your computer in any way using NPF's IP blocking feature.