The best time to set up ‘Pretty Permalinks’ is the moment you install your blog because if you already have a bunch of existing posts, changing the permalink structure will make it so that your old links to those posts will result in page not found errors - to fix this you would need to edit the .htaccess file to set up permanent redirects for each post and page in the form of:
Redirect 301 http://www.yoursite.com/index.php?p=2 http://www.yoursite.com/the-new-post-title.htm
This implies that the solution suggested in the previous post would not work, and a 301 redirect will have to be done for every post. Is this correct? And if so, is there an easy way to generate this mapping?