I need to be able to write/post links on the web that look like 'mysite.com/?d=foo', and take the user to filepath '/foo.php'. Here is my htaccess:

RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^([^/]+)/$ $1.php [L]

RewriteRule ^([^/]+(/[^/]+)*)/$ /$1.php [L]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5}|/)$
RewriteRule ^([^.]+[^/.])$ /$1/ [R=301,L,NC] 

Baically I need to "force" '/?d=' before the filename, kinda like I've already modded my htaccess to force a trailing slash. How do I need to reconstruct my htaccess to make that possible?