site redesign (changing from HTM pages to PHP)

website design, page names, 301 redirect

[SiteTutor]

We are redesigning our website and have built the new website in PHP. The old site is in htm. Most of the pages are new so they are not affected by the new code.

About half of the old pages in htm I want to include in the new website, however many of them are indexed in the search engines.

How do I add the old pages to the new site structure and not lose the indexed pages in the search engines?

Should I do a 301 redirect for each old page to each new page?

Should I leave up the old pages, and only add the new pages to the site map? (wouldn't this be considered duplicate content?)

should I use the same page names, but just change the extention. Please let me know your thoughts on this issue.

Thanks.

[Quadrille]

I'm not sure why you can't just keep them as they are, if you still need them?

If you change them - either to a different folder or htm > php, then SEs will see them as new pages, even if the content is the same. You can minimise damage by using 301s, but you can eliminate it by keeping the 'old' pages 'as is'.

If you cannot run the new system in a way that keeps the old pages, changing them over a period of time will also help to minimise ranking problems, as the site's overall ranking will be passed on through navigation as always to 'new' pages. But the little green bar will be gone for months. Note: this does not matter ;)