I'm trying to setup a twitter script that will update a users description, url, and photo.

I've got everything working where it will insert, I was trying to use the replace function but not having any luck, here's what I have so far:

Code:
$xml = new SimpleXMLElement($xmlstring);
$pimage = $xml->profile_image_url[0];
$pdesc = $xml->description[0];
$purl = $xml->url[0];

$process_profile = "REPLACE INTO twitter_cache SET twitter_user ='$twid', pimage = '$pimage', pdesc = '$pdesc', purl = '$purl'";
mysql_query($process_profile)
or die(mysql_error());