<?php
   if (!isset($_REQUEST["url"])) exit;

   $url = $_REQUEST["url"];
   if (substr($url, -0, 7) != "http://") exit;

   echo file_get_contents($url);
?>

AJAX by default only lets you play within your own Domain.com but there are plenty of times where you want to use someone else's feed.  Check out http://snipplr.com/view/12466/jquery-parse-rss-feed/ to understand the rest.

PHP: Capture RSS feed

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