Whether the browser can display these files or not is up to you. If you are running apache and the file extensions of your included files is ".inc", then you can keep the web server from feeding the file to the browser by changing your "httpd.conf" file with a generic directory directive for your http root like so:
<font color=blue>
<Directory /usr/local/etc/httpd/htdocs>
Options none
AllowOverride none
Controls who can get stuff from this server.
<Limit GET>
order allow,deny
allow from all
</Limit>
</font>
<font color=red>
<Files *.inc>
Deny from all
</Files>
</font>
<font color=blue>
</Directory>
</font>
-- Rich