File extension won't have an effect on SEO placement. Just make sure you are keywording your pages correctly. This doesn't mean META tags, which really don't hold much weight these days, but Title tags, ALT tags on images, and even Refs and Titles on your anchor tags will! Make sure that your pages' content is actually "about" what they say they are about; and consider embedding links, both internal and external - mix it up with linking words and phrases. Link to other sites that have to do with your content, and most important of all, don't be spammy.

(This is 2 years of working for an SEO company talking - SEO optimization strategy changes all the time, but follow those basics and you should be able to get a decent foothold in the ranking process).

Sorry for the ramble