it sounds to me like you have an index.htm page and an index.php page.
when you use site_url/ it is loading the .htm page instead of the php page.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.