My personal vote would be to nuke it from orbit and then rebuild it in a safer configuration.
No PC anywhere should be in use without anti-virus software. If necessary get AVG, but in reality go and pay for something decent. I personally like the version of ZoneAlarm with integrated Anti-Virus - that's a nice product and not too expensive.
Also.. ditch Internet Explorer. That's really one of the best and simplest (and cheapest) things that you can do. Hide the icon somewhere and use Firefox (or Opera.. or Mozilla) instead. Do the same for the mail client.. use Thunderbird, Eudora or something else.
Don't forget to patch the PC up to the very latest patches you can find. Really big ones like Service Packs are best applied from a CD after being downloaded on broadband.
