Ora dovrebbe funzionare bene 
Codice PHP:
<?php
$text=$_POST['testo'];
$sub=explode("\n",$text);
$tot=count($sub);
$i=0;
while($i<=$tot)
{
if(ereg("]",$sub[$i]))
{
$text=$sub[$i];
$pos=strpos($text, '[');
$nick=substr($text, 0, $pos);
$sub_text=substr($text,$pos);
$sub_text=str_replace("[","",$sub_text);
$sub_text=str_replace("]","",$sub_text);
$ex_text=explode(" ",$sub_text);
$tot_ex=count($ex_text);
$j=0;
while($j<$tot_ex)
{
$text_fine.= ":".$ex_text[$j].":";
if($j!=$tot_ex-1)
$text_fine.=" ";
$j++;
}
echo "$nick [$text_fine]
";
}
else
echo $sub[$i]."
";
$text_fine='';
$i++;
}
?>
<form method='POST' name='news'>
<textarea name='testo' cols='40' rows='6' class='form'></textarea>
<input type="submit" value="invia" />
</form>
Fammi sapere!!