well, if you know preg_replace, then you can make your own.
PHP Code:
function bbcode($message)
{
$bbcode = array(
"/\[img\]http:\/\/(.*?).(gif|jpg|jpeg|png)\[\/img\]/i" => "<img src='http://\\1.\\2' alt='User Posted Image' />",
"/\[img\](.*?).(gif|jpg|jpeg|png)\[\/img\]/i" => "<img src='http://\\1.\\2' alt='User Posted Image' />",
"/\[i\](.*?)\[\/i\]/i" => "<i>\\1</i>",
"/\[b\](.*?)\[\/b\]/i" => "<b>\\1</b>",
"/\[u\](.*?)\[\/u\]/i" => "<span style='text-decoration:underline'>\\1</span>",
"/\\n/i" => "<br />",
);
return preg_replace(array_keys($bbcode), array_values($bbcode), $message);
}