“You are not authorized to view this page” error 403

Hello. please can someone help as I am desperate to sort out this problem. I have come home to my parents house and they have Win 98 2nd edition on their computer and Internet Explorer version 6 installed, but when I go to download something or go to some webpages, I get the above error message, how can I stop getting this and access webpages as I can on my Win XP laptop?