You can add the following to the .htaccess file in your www directory:
<Limit GET>
order deny,allow
deny from 63.11.187.103
</Limit>
(change the ip address to the appropriate ip you wish to block)
This will block them from seeing not only your web pages, but any pages in subdirectories below the main site. If you wish to block them from seeing only one, or a small subset of, subdirectories, place the above code in the .htaccess file of the highest level directory that you want blocked.
