I moved from:
www.example.com/archives/month/day/entryname.php

to:
www.example.com/archives/month/entryname/

The easiest way to do this was with the Apache server mod_rewrite module, which is installed by most web hosts by default. Unfortunately, figuring out the mod_rewrite code to do this in my .htaccess file was tough, the learning curve is incredibly steep. I asked around forums and the WordPress support site.

Here is the code to add to you .htaccess file. You may need to adjust for your specific situation.

RewriteEngine On
RewriteBase /

RewriteRule ^archives/([0-9]{4})/([0-9]{1,2})/([0-9]{1,2})/(.*)\.php$ http://example.com/archives/$1/$2/$4 [R,L]

RewriteCond %{REQUEST_URI} ^archives/.*$
RewriteCond %{REQUEST_URI} !^.+\.php.*$
RewriteRule .* – [L]

Additional mod_rewrite tips and tricks to make sure your killer Page Rank and SEO work doesn’t go down the drain when moving your blog.