Cross Site Scripting Project

Essentially what I have is a situation whereby Site A contains an Iframe to Site B...within the Iframe on Site B there is a table that has a background property that refers to Site C. Site C is under my control and the page called in the property table is free to be edited by myself. What I need to creating is a script that sits on Site C that can redirect to a page on Site A. Previously there was only Site A and no Site B and no Iframe so I just used a simple PHP header function to redirect the user. I don't mind what language the script is in, PHP is preferred however. Remember this involves redirecting from within an Iframe.