PHP - BBCode parser - Parse both bbcode link tag and not tagged link

I need to do this :

when a user insert a BBCode tag, with preg_replace and regex i do some trasformation.

e.g.

function forumBBCode($str){
   $format_search=array(
      '#\[url=(.*?)\](.*?)\[/url\]#i'
   );

   $format_replace=array(
      '<a class="lforum" target="_blank" href="$1">$2</a>'
   );

   $str=preg_replace($format_search, $format_replace, $str);
   $str=nl2br($str);
   return $str;
}

now i want also this : when a user insert a normal text with a link, this must be trasformed too. i can't do this trought preg_replace function, because if i write a code as

$format_search
'#(www\..*?)#i'

$format_replace
'<a class="lforum" target="_blank" href="$1">$1</a>'

it will convert the link 2 time (in the [url] and when the link is without this tag).

so i think to this function :

    function checkLinks($string) {
    $arrelab="";
    $arr=split(' |\r\n', $string);
    for($i=0; $i<sizeof($arr); $i++) {
        echo $i." - ".$arr[$i]."<br/>";
        if ((strpos($arr[$i], 'www.')!==false) or (strpos($arr[$i], 'http://')!==false) or (strpos($arr[$i], 'ftp://')!==false)) {
            if (strpos($arr[$i], '[url=')===false) {
                $arr[$i]='<a class="lforum" target="_blank" href="'.$arr[$i].'">'.$arr[$i].'</a>';
            }
        }

        $arrelab=$arrelab." ".$arr[$i];
    }
    return $arrelab;
}

the problem is that i need a split as for the newline, as for the empty space. any help would be appreciated.

p.s. sorry for my bad english :)

cheers