are you only typing in/clicking on the main page http://www.fanfiction.net/ ?
i know many peoples list there myspace pages on their profiles as there homepages.
is it the main myspace page or a band/specific persons site?
try going to one of the sub-pages of fanfiction.net:
http://www.fanfiction.net/book/
http://www.fanfiction.net/anime/
http://www.fanfiction.net/movie/
http://www.fanfiction.net/forums/
http://www.fanfiction.net/communities/
http://www.fanfiction.net/search.php
http://www.fanfiction.net/dictionary.php
http://www.fanfiction.net/j/0/0/0/
http://www.fanfiction.net/secure/login.php
or a specific author or fic instead of the main page
it may be you do have malware/spyware but hopefully by going to one of these other pages you might be able to bypass it if you cant remove any outside problem