User Authorization question

I am setting up user authentication which is checked against a database.. for php files this is easy, I put a little include at the top of each file that checks for cookie and redirects to a form if not found... But.. most of my pages are .html and though I can include the authentication code with a SSI call, the page displays with the form at the top. Is there a way I can stop an html page from being sent to the browser from an included php script. I don't think I can do this, and have been thinking about it for a while, but I thought I would post here just to check!