General newb questions

Here’s the situation – I wanna use image links for some static pages with content not sourced via the WP engine, like about, contact, press, etc. I’d like the url to these pages to be about.php, contact.php, etc. When I add the content to these pages, I get errors about undefined function get_header(), etc. If I just manually include the header, then of course now I get undefined function blog_info since that function is called in the header. If I try to add a functions file from a different theme, it has undefined functions, and I can’t re-define the default WP functions or the general WP blog itself won’t work (index etc).

What do I do here? I’m trying to build a new theme and running into a wall. How do you add a static directly-linked page that still supports WP functionality?

Is it even possible? Should I just use a switch statement in index and $_GET[‘page_id’] ?