Three simple lines made it
// Permanent redirection
header("HTTP/1.1 301 Moved Permanently");
header("Location: http://www.flipthedolphin.com/");
exit();
?>
I just copied and pasted the above lines of code inside an empty file and renamed it to index.php, then putting it inside my /wordpress/ folder made the trick: no more 404 errors if someone visit www.flipthedolphin.com/wordpress/.
I found an interesting way to make redirects in ASP/VBscript, Javascript, ColdFusion and so on. Interesting stuff if you’re receiving many 404 from visitors that did not update their bookmarks (or if you’re losing readers because you changed the wordpress/feeds folder). Here it is: Permanent Redirect with HTTP 301.