Insert header/footer into non WP pages

I’m interested in integrating two php sites, WordPress and PHPiCal (www.phpical.net) so they essentially work as one site. I’ve got a good start, but I’d like to insert the wordpress header and footer (maybe the categories links) into my phpical pages. These pages reside in another folder on my server, so I’m not exactly sure how to do this. I’ve tried simly using the includes function, but I’m missing something as I don’t get back the header I expect. Anyone have any hints on displaying the wordpress header and footer outside of the servers wordpress folder?
Thanks!