function bbc2html($str) {
    $patterns = array( "/\[link\](.*?)\[\/link\]/", "/\[url\](.*?)\[\/url\]/", "/\[b\](.*?)\[\/b\]/", "/\[u\](.*?)\[\/u\]/", "/\[s\](.*?)\[\/s\]/", "/\[i\](.*?)\[\/i\]/", "/\[center\](.*?)\[\/center\]/", "/\[scroll\](.*?)\[\/scroll\]/"); 
    $replacements = array( "<a href=\"\\1\">\\1</a>", "<a href=\"\\1\">\\1</a>", "<strong>\\1</strong>", "<u>\\1</u>", "<s>\\1</s>", "<i>\\1</i>", "<center>\\1</center>", "<marquee behavior=\"scroll\" direction=\"left\">\\1</marquee>"); 
        $str = preg_replace($patterns,$replacements, $str);
    return stripslashes($str);
}
bbc2html($str);

k thnx