I'm not sure about individual files, but I know you can hide specific extension types.
Code:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^(.*)$ $1.php
Replace php with another file extension to change it, html, htm, asp
http://eisabainyo.net/weblog/2007/08...-via-htaccess/