The site has been up for several months and it has been linked to by a few sites. I'd like to change the index page from a static HTML page to a dynamic PHP page. I'd like to make the change with little (or no impact) on the current links and search engine ranking.

I've been considering changing the .htaccess so it will show PHP pages as HTML. It would seem that both goals of retaining established links and also allow dynamic pages. Any thoughts? Potential problems?

What would you advise?