Help! my IE Home Page infected

My Internet Explorer has been taken over by
C:\Searchpage.html. I cannot change the Home Page to
anything else. If I do it replaces it with
C:\Searchpage.html. We've deleted that document from the C: drive but it comes right back. We've ownloaded all the Windows Updates, including 832894. We've run the latest Norton Anit-virus and Spyware Nuker. Everything is clean. We followed the directions under Knowledge Base Article 320159. We changed the entry under Default_Page_URL under
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet
Explorer\Main to http:/www.msn.com and when we estarted the PC it is changed back to C:\Searchpage.html. Can anyone here help me? Thanks.