Fatal error: Call to undefined function: xslt_create()

[superbovine]

The Error:

Fatal error: Call to undefined function:  xslt_create() in /Users/cow/Sites/atom2rss/atom2rss.php on line 22

Verison:
Apache/1.3.33 (Darwin) PHP/4.3.9

<?

// atom2rss.php

// Atom2RSS PHP converter 1.0 (20040215)
// Converts Atom 0.3 feeds to RSS 1.0 ones
// (c) 2004 by Giovanni Riccardi
// http://www.composizioni.net/atom2rss

// Based on Atom 0.3 to RSS 1.0 by Antonio Cavedoni
// http://cavedoni.com/2004/02/rss1


// Set the MIME type to application/xml
//header("Content-type: application/xml");

// atom and xsl files
$atom_file = "atom.xml"; 	//set this to your actual atom file
$xsl_file = "rss1.xsl";

// create a new XSLT processor
$xh = xslt_create();

$fileBase = 'file://' . getcwd () . '/';
xslt_set_base ( $xh, $fileBase );

//echo "here";
// process the files
$rssfeed = xslt_process($xh, $atom_file, $xsl_file);
if (!$rssfeed) {
    echo 'XSLT error: ' .xslt_error($xh) ;
}
else {
    echo $rssfeed;
}
// free memory
xslt_free($xh);

?>

xslt shows up in my phpinfo. I have googled around for this problem with little help.