Alans version didn't seem to work right. If you're having the same problem consider using this slightly modified version instead:
function unhtmlentities ($string) {
$trans_tbl = get_html_translation_table (HTML_ENTITIES);
$trans_tbl = array_flip ($trans_tbl);
$ret = strtr ($string, $trans_tbl);
return preg_replace('/&#(\d+);/me',
"chr('\\1')",$ret);
}