can not change my ie 7 home page?

i have xp2, ie7, whenever i open internet explorer, it automaticaly open some web page http://www.nyd.zoomshare.com/, i try to change my home page to other, but still the above page is as my home page, then i can not download microsoft security explorer, can not download virus definition from norton, when try to download these, it gives the message your current security settings do not allow this file to be downloaded.