That looks OK to me.
Is this on a different page to the one you attached?
Having you got <?php session_start(); ?> at the top of the page so that the SESSION call can read the value?
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.