Control visibility based on user logged in, etc.

We'd like to add some things to templates (e.g. amember/templates/header.html) so that only logged in users can see them, or only users who have already purchased can see them. We used this code (found on the forum):

{php}
$logged_in=false;
if ($au=$_SESSION['_amember_user']){ $logged_in=true; }
{/php}

Which is ok. However we can't get this part right:

{php}
if($logged_in)
{
Echo "<li><a href=\"" . ($config.root_url) ."/../logout.php\">log out</a></li>";
Echo "<li><a href=\"" . ($config.root_url) ."/../member.php\">my account</a></li>";

}
else
{
Echo "<li><a href=\"" . ($config.root_url) ."/../login.php\">log in</a></li>";
}
{/php}

We'd like to print the "root_url" variable, but don't know how to do that using the templates. In the exising code, we see that this works: {$config.root_url}, but that doesn't seem to work inside {php} tags. What's the proper way to do this?

We tried the following:
<pre>
{php}
var_dump(get_defined_vars());
{/php}
</pre>
and it dumps a lot of variables, we just can't access them. We would like to know how we can get to stuff like "member"/"member_id", etc either from code within the {php} tags, or just in {if ...} tags.

Thanks in advance!