Grabbing partial file contents

[Anon]

I have a piece of e-commerce software that
spits out my store using static html files and templates which cannot be easily changed.

What I want to do is php3 enable the entire site using include files, rotating banners etc..

I can create all of the store in php3 but I need to 'grab' the product pages which are in htm format. I also need to grab only the contents of the htm files, that is whatever is between the body tags.

Essentially,
How can I easily open a htm file, and 'include' within my php3 only parts of such a htm file i.e only between point a and point b.

I will also need to do this often, should I create a funtion?

Thanks

Gary