[jQuery] Help getting started with JSON (and PHP)

[sso]

I need to return several values and I'd rather do it all in one ajax
call.  However there doesn't seem to be anything in data.  Perhaps I'm
way off here.

I appreciate any guidance you can give me.  Thanks :)

This is my jquery
        $('#cart-pulldown').livequery('click', function(event){
                $.getJSON(siteurl + "home/aj/showCart/", {},
                        function(data){
                                alert(data);
                        });
        });

This is the ajax in my PHP
                                $tmp = "";
                                foreach($_SESSION['cart'] as $key =>$line){
                                        $tmp .= $key . " ..... " . $line . "<br 
/>\n";
                                }
                                $tmp .= '<div><span id="clearList">Clear 
List</span></div>';
                                echo json_encode($tmp);