WordPress.org

Simple 301 Redirects provides an easy method of redirecting requests to another page on your site or elsewhere on the web. It's especially handy when you migrate a site to WordPress and can't preserve your URL structure. By setting up 301 redirects from your old pages to your new pages, any incoming links will be seemlessly passed along, and their pagerank (or what-have-you) will be passed along with them.

Note: The format for requests is '/about.htm' and the format for redirects is 'http://www.domain.com/about/' in order to emulate the way Apache handles 301 redirects and because while you can only accept requests to your site, you can redirect to anywhere.