RewriteEngine ON
RewriteRule ^/.+ / [L,R]
That will redirect everything to / as a permanent redirect. Look at http://httpd.apache.org/docs/2.0/mod/mod_rewrite.html for more information on the flags you can add for transparency etc etc.
If you want this in .htaccess
make sure you have the correct override directives in your <VirtualHost >
config.