rss twitter error help pls

Hi,
I am attempting to install " Post an RSS feed to twitter "
I get this error:
Fatal error: Call to undefined function: simplexml_load_string() in /home/ersparad/public_html/0twitter/twitterfeed.php on line 33

The line 33 is
$feed = simplexml_load_string ( curl_exec($ch) );

Your help is appreciated

You need php5 to use that function

Thank you... I have 4.4.4 I am having the web host install 5.
Thank you.