$sql = mysql_query("SELECT ip FROM `lentele` WHERE `id` = 'X'  "); 

while ($row = mysql_fetch_assoc($sql)) {	

$ip_list = explode(',', $row['ip']);

if (in_array($_SERVER['REMOTE_ADDR'], $ip_list)) {

echo 'tu jau balsavai bla bla bla.';

} else {

$ip = $_SERVER['REMOTE_ADDR'];

kodas kuris prideda taska ar kita suda.

...

mysql_query("UPDATE `lentele` SET `ip` = CONCAT(ip,',$ip') WHERE `id` = 'X'

");

}