I am needing help trying to extract data out of an XML using PHP.

I have the following simple page that is passed the following type of value for URI, http://www.google.com/calendar/feeds...gclr777v7bc46s

PHP Code:
if (isset($_GET['uri'])) {
} else
header'Location: http://www.rosmini.school.nz/facebook' ) ;
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Event Details</title>

I have no problem getting details like title and content but what I can't get is the start and end times which are buried in the fetch XML in <gd:when endTime='2011-10-26' startTime='2011-10-25'/>

I want to be able to do something like
PHP Code:
But when I look at the output of simplexml_load_file($uri), I can't see these values anywhere.