IE Pop Up Windows

I have a Win 2K P.C that is overcom by pop up windows with IE 5.5. I can reboot the p.c and not even have IE running, and 30 – 45 minutes later, ther will be 10-15 advertisements. I have scanned for a virus, and it checks clean with NAV. I looked for programs running in memory, and see nothing unusual. (I was looking for something related to i-won possibly.) Any suggestions?
P.S. I have added the Group Policy snap-in alreday but it shows un-configured.