If your are using their 'authentication file' method, then I think you will need to manually upload the file they provide to your site via FTP or via the File Manager in your host's control panel (if your host provides one).
If you can't upload the file to your hosting account, then it seems they have a Meta tag that you can add to your home page that can also be used for authentication, but they would have to verify this manually, see this from t
http://community.norton.com/norton/board/message?board.id=nis_feedback&message.id=80006
If this is the method that you need to resort to, and if your site's homepage is a ShopSite-generated page, you can add the Meta tag that they specify to your ShopSite-generated homepage using the method described in the following ShopSite Knowledgebase article:
http://support.shopsite.com/KBase/questions/1974/
-Loren