hit by virus,help please

The strange thing started a few days ago. Whenever I started IE, it doesn't go to my home page www.hotmail.com, it displays a search page, not from MSN; the left lower corner shows "Downlaoding picture http://mainsearchpage.com/images/img.JPG...". When I went to IE option to set home page again, next time it will set to "about:blank". I am sure this is a malacious virus but I couldn' find where it sits. Can somebody here land a hand?