Exec-php: calling a php from a post

I’m currently building a site and I’m looking to incorporate exec-php into it.

I’m trying to figure out how to make it so that I can call a php page to display where my entry normally would go, but not all the time. For example, some posts would display normally whereas other times I want to call a php page to display.

I’m new at php, so any help would be appreciated.

http://projectlightbox.gofreeserve.com/wordpress/?p=1

here is a link to show you want I mean – Normally if I would post it would show up in the white area (excerpt down below), but I want to call a php page to go in the white area.

Thanks!