We are in the process of re-designing our website (www.openxtra.com) and moving over to Apache/PHP/MySQL.
My question is: how important is it to retain our old site structure and URLs so far as the search engines are concerned?
Our old site used non-standard file extensions _html instead of .html. Should we retain the old file URLs to ensure that the SEOs don't get confused. If so, what should the old URLs contain? Should they just link to the new content or retain the old content?