[PHP] 404 Header Problems

I'm trying to issue a 404 header on one of my pages. But it does not redirect. I figured, with many function calls before it, that it might be outputting something to the screen before the header() command was issued. So, I tried issuing a 404 header from a new page, consisting of this

[PHP] 404 header

Hi I'm using IIS and I changed the 404 page to something else. Now the server returns an 200 OK message for a mistaken page :) Does anyone know the exact headers I need to send b4 the page so that the server will send back to the client the 404 NOT FOUND header along with the new page? thanks