Editing and Creating child pages… having a problem!

I have been trying to use an aggregated feed plugin on a child page but the ‘write page’ function forces me to add content using a post. i tried installing a plugin that would allow me to use php in a post but that’s not working at all. the code just disappears once i try to save it. i tried creating my own version of a child page form copying and renaming the index.php but if i do that the header function doesn’t work. i tried to ftp into the site to manually edit the child pages (and remove the posting action) but i can’t find these files in any of the folders. they don’t seem to exist.

i am at a loss as to what to do next.