Atom, what RSS Feed are you trying to get? You need to consider the crossdomain policy files and if the websites have it. Gamebuilder's feed was the only one I found that would actually work, so here's an alternative:
Write a PHP file:
<?php echo file_get_contents('url'); ?>
Put it on your website, then use my object to access the php file, which will look exactly like the one you're trying to reach. I did this and it worked.
You can test if you want with: http://www.triplezap.com/test.html
Just enter the url in the edit box and hit Go to see if one works!
An example with PHP is http://www.triplezap.com/test.php which is xkcd's RSS feed.
Oh also, you could just pass the URL you want into the PHP through GET, but you'd need to encode the URL first (which I believe the GET Object has), then your single PHP file would work with any RSS Feed.