This is a plugin I made for GetSimpleCMS.  I am currently working on it and you can find it for download here.

<?php
function tumblr()
{
$feed = simplexml_load_file('http://yournamehere.tumblr.com/api/read?type=post&start=0&num=4');
$posts = $feed->xpath("/tumblr/posts/post");
foreach ($posts as $post) {
    echo '<div class="article">';
    echo "<br/>";
    echo '<h3 class="article_title">'.$post->{'regular-title'}. '</h3>';
    echo '<p class="article_date">' .$post['date'].'</p>'; 
    echo $post->{'regular-body'};
    echo "<br/>";
    echo '<a href="'.$post['url']. '">Read More</a>';
    echo "</div>";
}
}
?>
<? tumblr() ?> 

This sets up the function, and how how to use the function, simply put your tumblrname in where "yournamehere" is. I will update this further as I learn more. This was my first attempt at using xpath or simplexml where are all new to PHP since I learned it back in 2003-2004.