.htaccess書き換えルール

これを試して私に知らせてください。

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule ^profile/([^/])/? profile.php?username=$1 [L,NC]

RewriteRule ^login/submit$ login.php?action=submit [L,NC]

# /login/ will go to login.php or /contact/ will go to contact.php
RewriteRule ^([a-z0-9_\-]+)/? $1.php [L,NC]

Here's the full documentation about the [] flags: http://httpd.apache.org/docs/2.3/rewrite/flags.html