All this nightmare would not exist IF Mr. Bill Gates was honest enough to protect his operating system from invasive software. Back in 1975 the DEC systems I worked with, were protected not only against invasive software, but also against programmer's errors which could damage the system area. Windows allows anybody to modify Windows Registry (the most intimate system files), install themselves as privileged tasks, connect to Internet, report your activity to their headquarters, disable your anti-virus software, etc. They don't destroy your disk because they want you alive, not because they can't.
For the moment, use a firewall like ZoneAlarm, use AdAware, set your I.Explorer Security to High, block cookies, avoid Kazaa and similar music-sharing programs, avoid MS Messenger, don't allow your PC to act as a server, don't open unsolicited mail, and pray.